bluuebunny/crossref_metadata_2025 huggingface dataset:
Orbital interactions. XII. Product studies and competition kinetic measurements of the Birch reduction of a series of hexahydrodimethanonaphthalenes and their interpretation in terms of orbital interactions through space and through bonds
Authors: Chau DD , Paddon-Row MN , Patney HK
Published: September 2010

Relative rate constants for the Birch reduction (Li/liq. NH3/ButOH) of the three isomeric
hexahydrodimethanonaphthalenes (3)-(5) and the octahydro analogues (10)-(13) were obtained
and compared with those obtained for the reduction of norbornadiene and norbornene from an
earlier study. Diene (5) was reduced almost 2000 times more rapidly than norbornene and 20000
times more rapidly than the monoene (13). Rate-enhancement factors for dienes (3) and (4) were less
substantial but meaningful: 19 for (3) [compared with (10)] and 35 for (4) [compared with (12)].
These rate enhancements were attributed to the operation of π* orbital interactions through space in
diene (5) and to the presence of π* orbital interactions through four bonds in dienes (3) and (4). The
existence of a linear relationship between the natural logarithm of the rate of reduction of a substrate
and its LUMO energy (obtained from either gas-phase electron affinities or ab initio MO calculations)
supports this conclusion. The only-fair correlation of the above relationship was attributed to the
neglect of other factors, such as the electronic structure and the geometry of the anion radical, which
contribute to the overall rate of the Birch reduction. These two factors were explored by using
PMO theory and ab initio MO calculations. In particular, full geometry optimizations (UHF, STO-3G
basis set) on the anion radicals of norbornadiene (1) (C2v symmetry constraint) and norbornene (22)
(Cs symmetry constraint) were carried out, and their geometries reported. Noteworthy is the strong
pyramidalization of the olehic centres of (1) and (22) in the endo direction. These pyramidalizations
explain the observed stereoselective exo protonation of the anion radical of (1), and also the much
faster rate of reduction of (1) compared with (5), since the pyramidalization in the anion radical of (5)
is such as to hinder protonation. The geometries of anion radicals appear to have a profound effect
on rates, on stereoselectivity of protonation, and on the structures of the final products, and this
is discussed in detail. The synthesis of the diene (3) is also described.
Central nervous system active compounds. XII. The synthesis and properties of 3-dimethylaminomethylene phthalides
Authors: Clarke SI , Kasum B , Prager RH , War AD
Published: September 2010

Isobenzofuran-l(3H)-one (phthalide),
and its derivatives react with dimethylformamide dimethyl acetal to form
3-dimethylaminomethyleneisobenzofuran-1-one and minor amounts of the corresponding
internal betaine 2-(2-carboxylatophenyl) ethynyltrimethylammonium. The use of t-butoxy-
is(dimethylamino)methane allows the isolation of the corresponding aminal, which readily loses dimethylamine on recrystallization. The dimethylamino group in the title
compounds is replaceable by amino, hydrazino or
hydroxy groups in mildly acidic solution. 3-Formylphthalide, the tautomer of the last-named product, could be isolated as
the 2,4-dinitrophenylhydrazone.
The effect of weathering on the 1600 cm-1 band of bituminous coal
Authors: Johnson RA , Cooney RP
Published: September 2010

The 1600 cm-1
band intensities in the infrared spectra of Australian bituminous coals, of a
range of rank, exposed to natural weathering conditions have been monitored
over a period of 11 months. Periodic increases and decreases in intensity were
observed under these conditions. The results of a subsequent oxidation study at
353 K suggest that some of the observed changes may be due to changes in
radical concentrations.
Coordinated fluoride in rhenium(I) carbonyl complexes
Authors: Horn E , Snow MR
Published: September 2010

Bromide abstraction from
the complexes Re(CO)3L2Br (where L = SbPh3 and
L2 = bpy, dpe, tmen)* by AgF2H gives the corresponding fluoro compounds Re(CO)3L2F. Mass
spectra and structural data show that the fluoride in these complexes is
coordinated to the metal. The structures of Re(CO)3(tmen)F
and [Re(CO)3(tmen)F]2H.HOBF3
are reported here. Crystals of Re(CO)3(tmen)F
are monoclinic, space group P21/c, with a 8.202(2), b 13.115(9), c 12.048(4) � and β 102 24(3)�. A
full-matrix least-squares refinement by using the absorption corrected data
gave a conventional R value of 0.041. [Re(CO)3(tmen)F]2H.HOBF3
also crystallizes in the space group P21/c. The lattice parameters
are: a 17.495(2), b 10.772(2), c 15.447(1) � and β ( 101.409(8)�. The final R value of a
blocked least-squares calculation converged at 0.061. In these two complexes
the simple Re-F distance is 2.040(4) �, in Re(CO)3(tmen)F. The Re-F distance is increased to 2.236(10)�, as a
result of hydrogen bonding between the fluoride and HOBF3 in the
latter compound.
Oxidative cyclizations. VI. Mechanism of cyclization of N-chloro-2-nitroanilines to benzofuroxans under alkaline conditions
Authors: Chapman KJ , Dyall LK , Frith LK
Published: September 2010

An improved synthesis of
N-chloro-2-nitroanilines used chlorine in CCl4 solution to halogenate the 2-nitroaniline. Treatment of these CCl4
solutions of the N-chloroamines with methanolic lithium methoxide, or
potassium t-butoxide in t-butyl alcohol, produced a transient red colour, and quantitative yields of the corresponding benzofuroxan (benzofurazan
1-oxide) were obtained. U.v. and e.s.r. spectra
indicated that the red species is the conjugate base of the N-chloroamine. On the basis of rate measurements, it is
concluded that this red anion ejects chloride ion irreversibly to yield a
singlet ortho-nitrophenylnitrene,
which then rapidly cyclizes to the benzofuroxan. The ortho-nitro
group does not assist in chloride ion ejection.
N-Substituted enaminones from 3-aminobutenoic acids and 1,4-naphthoquinones
Authors: Parr RW , Reiss JA
Published: September 2010

N-Substituted
3-aminobut-2-enoic acid esters (enaminones) were
prepared by condensing methyl (or ethyl) acetoacetate
with (2,2-dimethoxyethyl)amine, (4,4-dimethoxybutyl)amine, N-(2'-aminoethyl)-pyrrolidine and
N-(2'-aminoethyl)morpholine to produce enaminones
(3)-(6) respectively. A cyclic enaminone (11) was
prepared from dimethyl acetylenedicarboxylate. The N-substituted amino quinones
(12)-(14) are also reported, together with their 13C n.m.r. data and
assignments.
Stereospecific formation of tetrahydrofurans from substituted 2,8-Dioxabicyclo[3.2.1]oct-3-ylmethanols
Authors: Abell AD , Dimitriadis E , Massy-Westropp RA
Published: September 2010

The reactions of some
substituted 2,8-dioxabicyclo[3.2.1]oct-3-ylmethanols (hydroxy acetals) with oxalic
acid in aqueous methanol solution gave tetrahydrofurans
stereospecifically in good yields.The reactions occur with
inversion of configuration at a tertiary carbon and are considered to proceed by
a mechanism involving the carbonyl group generated by hydrolysis of the acetal
function.
The extraction of iron(III) from 6 M hydrochloric acid by long-chain amines dissolved in chloroform
Authors: Ilic MZ , Cattrall RW
Published: September 2010

Two-phase titration studies
demonstrate a strong tendency for the formation of heterogeneous aggregates in
the extraction of iron(III) from 6 M HCl by primary, secondary and tertiary
amine hydrochlorides in chloroform. The stoichiometries of the extracted complexes
are identified, and their extraction equilibrium constants are reported. The
importance of the reagent monomer in the extraction process is discussed.
The preparation and reactivity of arylbismuth(III) dicarboxylates and diarylbismuth(III) carboxylates
Authors: Deacon GB , Jackson WR , Pfeiffer JM
Published: September 2010

The compounds R2BiO2CR'
(R = Ph, p-MeC6H4, p-MeOC6H4,
p-EtOC6H4 or C6F5; R' = Me or CF3)
and RBi(O2CR')2 (R = Me, Ph,
p-MeC6H4, p-MeOC6H~ or p-EtOC6H4; R' = Me
or CF3) are formed on acidolysis of the
corresponding triarylbismuthines in ether. The products were readily identified by 1H
n.m.r. spectroscopy, even in complex mixtures, because of the successive downfield
shifts of the aromatic resonances as the number of aryl groups decreases. By
contrast with triarylbismuth compounds,R3-n Bi(O2CR')n
(R = aryl; n = 1 or 2) complexes are readily hydrolysed,
whereas MeBi(O2CMe), is oxygen-sensitive
but more stable to hydrolysis. The compounds undergo aryl redistribution
reactions in dimethyl sulfoxide.
Evaluation of fluorescent materials for colour control of peroxylate chemiluminescence. IV. Fluorescence quantum yields of some phenyl and phenylethynyl aromatic compounds
Authors: Hanhela PJ , Paul DB
Published: September 2010

The fluorescence quantum
yields of 32 phenyl- or phenylethynyl-substituted
aromatic compounds have been determined in benzene using quinine sulfate as the
reference standard. Correlation with available data for the primary members of
the three groups of compounds, 9,10-diphenylanthracene, 9,10-bis(phenylethynyl)anthracene
and 5,12-bis(phenylethynyl)naphthacene was good. The
bis- (phenylethynyl) anthracenes showed little
variation in fluorescence efficiency within the series and high quantum yields
of the order of 0.7-0.9 were observed. Steric interactions in 9,10-diphenyl-anthracene
derivatives substituted in 1,4-positions lead to a significant reduction in
quantum yield. 1,4-Bis(phenylethynyl)naphthalene (Q 1.0) is considered to rank
with the most efficient of known fluorescent materials.
Competitive adsorption of sensitizer and electron transfer agent in an aqueous photolysis system
Authors: Furlong DN , Tricot Y , Swift JD , Sasse WHF
Published: September 2010

Tris(2,2'-bipyridine)ruthenium(II) dichloride, ru2+,
and methylviologen, mv2+, have been shown
to adsorb strongly onto negative surfaces of silica and dhp
vesicles. When both ru2+ and mv2+ are present in an
aqueous solution mv2+ demonstrates the higher affinity for
adsorption. The distribution of ru2+ and mv2+ between the
'adsorbed' and 'bulk solution' states has been found to dramatically affect
hydrogen production from a photolysis mixture in which these components
function as sensitizer and electron transfer reagent, respectively. In the
adsorbed state, charge separation is diminished and reaction of mv+ with platinum catalyst retarded. Enhanced
adsorption of mv2+ may render that left in solution more prone to
hydrogenation at the metal catalyst surface.
Oxidations of aromatic amines by superoxide ion
Authors: Crank G , Makin MIH
Published: September 2010

Superoxide ion acts as a mild and highly selective oxidizing
agent for aromatic amines. Aniline and α-naphthylamine
were not oxidized, but β-naphthylamine formed dibenzo[a,h]phenazine,
dibenzo- [a,i]phenazine and 2,2'-azonaphthalen-1-ol. o-and p-Diamines are oxidized to diaminoazobenzenes
but m-diamines
are unreactive. Similarly o- and p-aminophenols are oxidized to dihydroxyazo-
benzenes but m-aminophenols
are unaffected, and o-mercaptoaniline forms the disulfide. The oxidations are
considered to be free-radical processes, initiated by hydrogen abstraction by superoxide from the substrates. The biological significance
of the results is discussed.
The silver(I)-copper reaction in acetonitrile-water mixtures
Authors: Hughes FJ , Ritchie IM , Singh P
Published: September 2010

An electrochemical and kinetic study of the silver(I)-copper displacement (cementation) reaction in
acidified acetonitrile-water mixtures is reported. The cathodic polarization curves for the reduction
of silver(I) were found to be those of a fast electrochemical reaction. From the variation of limiting
current with rotation speed, the diffusion coefficient of silver(I) as a function of acetonitrile concen-
tration was determined. The anodic oxidation of copper gave a Tafel slope of 60 mV per decade
of current and was rotation-speed-dependent. It is suggested that the slow step in the reaction
mechanism is the diffusion of copper(I) from the electrode surface. At all acetonitrile concentrations
investigated, the two polarization curves intersected at a point where the current is fixed by the
diffusion of silver(I); this suggests that the displacement reaction will be diffusion-controlled,
which was confirmed by kinetic studies.
Provided the silver deposit was not too thick, there was good agreement between the measured
kinetic rate and that calculated from the silver(I) limiting-current measurements. However, when
the deposit became too thick, some increase in reaction rate due to surface roughening was observed.
A simple method of calculating the molecular rotations of the sulfur, nitrogen and phosphorus analogues of α-D-glycopyranoses having different substituents at the anomeric carbon atom
Authors: Poh B
Published: September 2010

The values of m and I of equation (1) for several series of α-D-glycopyranoses having different substituents at the anomeric carbon atom have been obtained earlier. From these values,
the molecular rotations of the corresponding sugars containing a sulfur,
nitrogen, or phosphorus atom in the ring have been calculated and found to
agree satisfactorily with the corresponding literature values.
Mechanistic aspects of diazaquinone chemiluminescence
Authors: Paul DB
Published: September 2010

Twelve cyclic hydrazides of
aromatic and heterocyclic o-dicarboxylic
acids were converted into diazaquinones by treatment
with t-butyl hypochlorite. Chemiluminescence was
produced from all diazaquinones on treatment with HO2-
derived from hydrogen peroxide and potassium hydroxide. Diazaquinones
derived from pyridine and pyrazine o-dicarboxylic
acid hydrazides afforded chemiluminescence with
hydrogen peroxide alone. Such nitrogen bases and N-oxides increase the nucleophilicity of hydrogen peroxide by complex formation
and this effect was also exemplified by observation of chemiluminescence
from phthalazine-1,4-diones, hydrogen peroxide and either pyridine or pyridine
N-oxide. Highly reactive diazaquinones emit light
with aqueous alkali and oxygen. No chemiluminescence
was produced with organic bases and oxygen which suggests the involvement of a
different mechanism compared with the hydroperoxide anion case.
Diarylheptanoid and other phenolic constituents of Centrolobium species
Authors: Jurd L , Wong RY
Published: September 2010

The heartwood of a specimen
of Centrolobium tomentosum Benth
(Leguminosae) has given (–)-centrolobine (1a), (–)-de-O-methylcentrolobine
(1b), (–)-centrolobol (2), piceatannol (3)and the isoflavone
formononetin (4). The heartwood of a second Centrolobium species, which could not
be identified further at the U.S. Forest Products Laboratory, yielded
(+)-centrolobine, (+)-de-O-methylcentrolobine, (+)-centrolobol, formononetin,
4',7-dihydroxyflavanone (5), 3-hydroxy-9-methoxypterocarpan (6) and minor
amounts of a new dihydric phenol. This was identified by n.m.r. and X-ray
diffraction measurements as 2-(2'-hydroxy-4'-methoxyphenyl)benzofuran-6-ol (8).
The preparation of (Methylthio)- and (Methylseleno)-tri(alkyl or aryl)phosphonium salts and their reactions with carboxylic acids and alcohols
Authors: Haynes RK , Indorato C
Published: September 2010

A series of (methylthio)-
and (methylseleno)-triphenylphosphonium salts and the analogous
tributylphosphonium salts have been prepared by methylation of the
corresponding tertiary phosphine sulfides and selenides. Details of their 1H,
13C and 31P n.m.r. spectra are given. Whereas the
(methylthio)- and (methylseleno)-triphenylphosphonium salts undergo rapid
decomposition in the presence of tertiary ammonium carboxylates or tertiary
amines, the (methy1thio)- and (methylseleno)-tributylphosphonium salts convert
such carboxylates into methanethiol and methaneselenol esters in acceptable
yields. A tris(dimethylamino)(methylthio)phosphonium salt, on the other hand,
converts benzoate into methyl benzoate in quantitative yield. Inferior yields
of (methy1thio)- and (methylseleno)-alkanes are obtained from two primary
alcohols and the tributylphosphonium salts.
The photochemistry of α-nitrostilbenes and related compounds. A study of double bond cleavage following intramolecular cyclization and nitro-nitrite rearrangement
Authors: Grant RD , Pinhey JT , Rizzardo E
Published: September 2010

A detailed study of the
photochemistry of a number of α-nitrostilbenes
is reported. The previously described intramolecular cyclization of (1) which
resulted in cleavage of the double bond was not found to occur to any extent in
the other compounds examined. The majority of the compounds were found to yield
significant amounts of aldehydes and nitriles, which
result from a new fragmentation pathway arising from initial photochemical
nitro-nitrite isomerization.
Pinching group stabilization. The synthesis and thermal isomerization of 10-Oxapentacyclo[6.3.2.13,6.01,8.02,7]tetradeca-4,12-diene
Authors: Butler DN , Russell RA , Waring RB , Warrener RN
Published: September 2010

Sensitized irradiation (benzophenone, 0�, N2, pyrex
filter, medium pressure Hg lamp) of dimethyl tricyclo[4.2.1.02,5]nona-3,7-diene-3,4-dicarboxylate
(11) in (E)-1,2-dichloroethene yielded a mixture of 1 : 1 adducts (13) and (14)
by site selective [2 π+2 π] cycloaddition at the cyclobutene π-bond. Reduction of the (Z)-dichloro isomer(13) with lithium aluminium hydride formed the related diol (16) which is the immediate precursor to the cyclic
ether (18). Dechlorination of (18) with zinc in
ethanol forms the title diene (19). Thermolysis of the polycyclic diester
(20) affords the fragmentation products cyclopentadiene
and dimethyl benzene-1,4-dicarboxylate. In contrast, the title compound (19)
containing the cyclic ether ring was more stable and yielded the novel isomer
(28) as the major product only upon flash vacuum pyrolysis at 560�(1.5 × 10-2
Torr). This difference in behaviour is attributed to
a pinching group effect exerted by the cyclic ether present in (19).
Structural studies in the lepidopterene system
Authors: Becker H , Hall SR , Skelton BW , White AH
Published: September 2010

.A new, metastable phase of lepidopterene, (5,6,11,12-tetrahydro-4b,12[1',2']:6,10b[1",2"]-dibenzenochrysene) (1), has been obtained from methylene chloride solution, exhibiting a luminescence
which differs from that of the stable form, having an absorption maximum at 580 nm rather than
560 nm. Single crystal X-ray diffraction determination of the structure of the new phase shows
it to be orthorhombic, Pbcn, a 36.75(3), b 7.229(7), c 44.85(3) Ǻ, Z 24, the structure being refined
to a residual of 0.065 for 2413 independent 'observed' reflections. Despite the relatively low precision
of the determination, it is evident that in the metastable form, the gross molecular disposition is
severely distorted. The crystal structure of dimethyllepidopterene (2) has also been determined,
and refined by least squares to a residual of 0.041 for 632 'observed' reflections. Crystals are mono-
clinic, P21/c, with a 9.607(4), b 11.564(7), c 10.576(6) Ǻ, β 107.72(4), Z 2; the molecules are
centrosymmetric.
Tetrachlorolepidopterene (31, formed by the dimerization of 1,5-dichloro-9-anthrylmethyl,
yields two crystalline forms from xylene and methylene chloride solutions which differ in their
crystal exciplex luminescence, showing emission maxima at 590 and 575 nrn respectively. Single-
crystal X-ray structure determination confirms that the two crystalline forms, α- and β-, are polymorphs of the same centrosymmetric molecular species. For the α-form, crystals are triclinic, P1 ,
a 15.374(6), b 9.858(4), c 8.000(4) Ǻ, α 83.98(4), β 83.73(3), γ 71.53(3)°, Z 2, 2138 independent
'observed' reflections being refined to a residual of 0.037; the unit cell contains two independent
centrosymmetric molecules. For the β-form, crystals are monoclinic, C2/c, a 11.03(2), b 13.67(2),
c 16.32(3) Ǻ, β 1 1 1.13(12)°, Z 4; the residual for 1554 independent reflections was 0.053.
On the molecular conformation of (E)-1,2-Di(9-anthryl)ethene. X-ray structure analyses of the parent compound and its 10,10'-dibromo derivative
Authors: Becker H , Engelhardt LM , Hansen L , Patrick VA , White AH
Published: September 2010

Two non-planar ground state conformations
have been established by X-ray diffraction analyses of (E)-1,2-di(9-anthryl)ethene (1) and its 10,10'-dibromo derivative (2). The
parent compound is characterized by a twofold axis of symmetry, the angle
between the plane of the anthracene and that of the ethene
being 55.1�. The angle between the two anthracene π-systems is 69.8�. The dibromo
derivative (2) is characterized by a centre of symmetry, and the two anthracene
π-systems are aligned parallel. The angle
of twist between the plane of the anthracene and that of the ethene is 60.7�.
The structure of 19αH-Lupeol methyl ether from Chionochloa bromoides
Authors: Pauptit RA , Waters JM , Rowan DD , Russell GB , Connor HE , Purdie AW
Published: September 2010

The structure of l9αH-lupeol
methyl ether isolated from Chionochloa bromoides has been determined by 13C n.m.r.
spectroscopy and X-ray diffraction. Crystals of the triterpene
are monoclinic, space group P21, with a 8.071(1), b
14.5477(6), c 11.6061(4) �, β
104.466(5)�, V 319.6 �3 and Z 2. The structure was solved by direct
methods, and was refined to R 0.054 for 1092 observed reflections. Previous
reports of synthetic and naturally occurring 19αH-lupanes are briefly
discussed, as is the distribution of the chemotaxonomically
discriminating triterpene methyl ethers in Chionochloa.
Imidazo[1,2-a]pyrazine, bromo and methoxy derivatives: a 13C N.M.R. determination applied to nucleophilic substitution studies
Authors: Bonnet PA , Sablayrolles C , Chapat JP
Published: September 2010

The 13C chemical
shifts and coupling constants of imidazo[1,2-a]pyrazine and some of its
derivatives are reported and compared with those of other series. These data
enable us to study the nucleophilic substitution of
3,5-dibromoimidazo[1,2-alpyrazine and 6,8-dibromoimidazo[1,2-a]pyrazine by a
methoxy group.
A structural study of the complexation of sodium ion by N,N,N',N',2,2-Hexamethylpropanediamide
Authors: Lincoln SF , Hambley TW , Hounslow AM , Maeji NJ , Snow MR
Published: September 2010

The structure of the
polymeric species of the stoichiometry Nan(Me2NCOCMe2CONMe2)2n(ClO4)n
has been determined in the solid state by X-ray diffraction methods. Each Me2NCOCMe2CONMe2
acts as a bridge between two sodium atoms by coordination through oxygen.
Each sodium atom is coordinated by four such bridging ligands and by one perchlorate such that the geometric arrangement of the five
oxygen atoms about the sodium atom is intermediate between a trigonal bipyramid
and a square pyramid.
Crystal structure of μ-Oxo-bis-fac-[triaqua-1,10-phenanthrolineiron(III)] Tetrakis(nitrate) monohydrate
Authors: Healy PC , Patrick JM , White AH
Published: September 2010

The crystal structure of
the title compound, [(OH2)3(phen)FeOFe(phen)(OH2)3](NO3)4.(H2O)(phen
= 1,10-phenanthroline), has been determined by single-crystal X-ray diffraction
methods at 295 K, being refined by
least-squares methods to a residual of 0.059 for 3467 independent 'observed'reflections. Crystals are monoclinic, P 21/c,
a 18.202(6), b 9.771(4), c 19.459(7) �,
β 94.46(3)�, Z = 4. Two of the four anions are disordered. Within the
cation, the geometry is typical of high-spin iron(III). O(bridge)-Fe are
1.765(4), 1.784(4) �, with Fe-O-Fe 162.0(3)�. The three water molecules in the
coordination sphere of each iron atom are fac; those trans to the O-Fe bond have long Fe-(OH2) distances
[2.154(5), 2.125(5) �] compared to those trans to the phenanthroline
chelates [2.028(5)-2.037(5) �]. Fe-N range from
2.143(6) to 2.166(6) �.
The 13C N.M.R. spectra of some arenetricarbonylchromium compounds, and their dicarbonyl triphenylphosphine, triphenyl phosphite and diphenylphosphinite analogues, including chelate compounds
Authors: Jackson WR , Rae ID , Wong MG
Published: September 2010

A number of new
arenetricarbonylchromium compounds have been synthesized in which the arene
ring is substituted with a number of large groups such as t-butyl. Also
prepared were the Ph3PCr(CO)2 and (PhO)3PCr(CO)2
analogues of these compounds and of more lightly substituted arenes, and a
number of chelate compounds incorporating a short chain attached at C1 of the
arene and bonded to chromium by phosphine, phosphite or phosphinite phosphorus
atoms. The 13C n.m.r. spectra of these compounds have been recorded,
and examined for evidence of stereo-specific influences of phosphorus on the
chemical shifts of the arene ring carbons, but no such effects were found. 31P
n.m.r. chemical shifts are also reported for these compounds.
Tetracyanonickelate(II) compounds of some (tetraazamacrocycle)nickel(II) cations. The structure of catena-Di(μ-cyano)dicyano(N-meso-5,7,7,12,14,14-hexamethy1-1,4,8,11-tetraazacyclotetradeca-1, 11-diene)dinicke1(II) hydrate
Authors: Gainsford GJ , Curtis NF
Published: September 2010

Tetracyanonickelate(II) compounds of several (tetraazamacrocycle)nickel(II)
cations have been prepared. The structure of the N-meso-5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-
4,11-diene, hmtd, compound [Ni(hmtd)Ni(CN)4].H2O
has been determined by X-ray diffractometry [monoclinic, a 1780.3(3), b
1063.41(7), c 1409.3(2) pm, β 120.54(1)�,
24, space group C2/c, R 0.021, Rw 0.030
for 2178 reflections] and shows a chain polymeric structure with trans singlet
ground state [Ni(CN)4]2- groups linking parallel stacked
triplet ground state [Ni(hmtd)]2+ groups.
The triplet ground state nickel(II) ions have a tetragonally
elongated coordination environment [Ni-N (mean macrocycle) 204.5(1) pm, Ni-N
(N≡C) 220.7(1) pm]. Tetracyanonickelate compounds of
macrocycles related to hmtd but with different
substituents, macrocycle ring size, and/or numbers of imine
and amine donor groups were prepared. Some are diamagnetic, with discrete
cation and anion, while others are similar to the hmtd
compound, and for the latter, tetragonal distortions were evaluated from the
reflectance spectra. Magnetic susceptibilities and infrared spectra are
reported.
Synthesis of substituted 9-Oxo-9,10-dihydroacridine-4-carboxylic acids. I. Factors affecting the direction of ring closure of substituted N-(2-Carboxyphenyl-amino)benzoic acids
Authors: Stewart GM , Rewcastle GW , Denny WA
Published: September 2010

The cyclodehydration
of 16 substituted N-(2-carboxyphenylamino)benzoic acids to substituted 9-oxo-9,10-dihydroacridine-4-carboxylic
acids with conc. H2SO4, POCl3 and ethyl
polyphosphate (epp) has been studied by h.p.l.c. Direction of ring closure can be qualitatively
interpreted in terms of the electronic and steric effects of the substituent
group on the carbonium ion intermediate formed from
the carboxylic acid group on the same ring as the substituent. Judicious choice
of substituents and cyclizing reagents can provide a
large excess of one isomer; hence this is a simple route to certain substituted
9-oxo-9,10-dihydroacridine-4-carboxylic acids.
3-Amino-5-hydroxybenzoic acid in antibiotic biosynthesis. VIII. Synthesis of chlorinated analogues
Authors: Becker AMRRW
Published: September 2010

The three isomeric ring monochlorinated derivatives of 3-amino-5-hydroxybenzoic
acid (1), required for studies of the biosynthesis and synthesis of several
important classes of antibiotics, are prepared from methyl
3-amino-5-hydroxybenzoate (5). N-Chlorosuccinimide selectively monochlorinates the 2- and 6-positions of this substrate,
whilst perchlorination followed by hydrolysis and regiospecific protodechlorination
at the 2- and 6-positions affords the 4-chloro acid.
Synthesis of the lichen depsides pseudocyphellarin A and B
Authors: Elix JA , Lajide L
Published: September 2010

The total synthesis of the
fully substituted lichen depsides, pseudocyphellarin A
(3-hydroxy-4-methoxycarbonyl-2,5,6-trimethylphenyl
3-formyl-2,4-dihydroxy-5,6-dimethylbenzoate) (1) and pseudocyphellarin B
(3-hydroxy-4-methoxycarbonyl-2,5,6-trimethylphenyl
2,4-dihydroxy-3-hydroxymethyl-5,6-dimethylbenzoate) (2) is described.
An X-ray photoelectron spectroscopic study of the oxidation of chalcopyrite
Authors: Buckley AN , Woods R
Published: September 2010

The oxidation of fracture
surfaces of chalcopyrite has been investigated by means of X-ray photoelectron
spectroscopy. Exposure of chalcopyrite to air resulted in iron becoming
concentrated at the surface of the mineral to form an iron hydroxy-oxide. The sulfur
spectrum of an oxidized surface, determined at 150 or 295 K, displayed new
intensity at the high binding energy side of the peak arising from unaltered
chalcopyrite. This is interpreted in terms of the formation of a sulfur-rich
copper sulfide of stoichiometry CuS2.
Extended exposure to air resulted in the formation of sulfate and copper(II).
The products of oxidation of chalcopyrite in air-saturated ammonia solution
were the same as those observed during exposure to air. Iron and some copper
were dissolved in the oxidation in acid media and the resultant surface layer
had a composition near Cu0.8S2 Reaction of an
acid-leached surface with hydrogen peroxide produced elemental sulfur in
addition to a metal deficient copper sulfide.
Quinones and quinone methides. X. The crystal structure of a dimeric oxidation product from 2,4-Bis(1,1-dimethylethyl)-6-[(4-methoxyphenyl)methyl]phenol
Authors: Wong RY , Jurd L
Published: September 2010

The molecular structure of
a minor oxidation product of the insect sterilant
2,4-bis(1,1-dimethylethyl) 6-[(4-methoxyphenyl)methyl]phenol has been
established as (�)-cis-1,3,6,8-tetrakis(1,1-dimethyl-ethyl)-4b,9b-bis(4-methoxyphenyl)-4b,9b-dihydrobenzofuro[3,2-b]benzofuran by means of X-ray crystallographic analysis.
Trapping of the Intermediate Formed in the E1cB Hydrolysis of Some Alkyl and Aryl N-(4-Nitrophenyl) carbamates in a Hydroxy Functionalized Micelle
Authors: Broxton TJ
Published: September 2010

The basic hydrolyses of some alkyl and aryl N-(4-nitrophenyl) carbamates in the presence of micelles of cetyl (2-hydroxyethyl) dimethylammonium bromide ( chedab )were studied. For compounds which react by the BAC2 mechanism, verysimilar results were obtained in cetyltrimethylammonium bromide ( ctab ) and in chedab micelles. However, for compounds which react by the E1cB mechanism, the intermediate p- nitrophenyl isocyanate was trapped by the hydroxy group of the functional micelle to form a new carbamate directly bound to the detergent molecules of the micelle. It was shown that this new carbamate decomposed by a BAC2 mechanism. p- Nitrophenyl isocyanate added to an alkaline solution of chedab gave N-(4-nitrophenyl)- carbamate ion. Thus, the isocyanate has to be generated within the micelle for trapping to occur. The rate of reaction of p-nitrophenyl isocyanate with OH-/H2O is faster than the rate of solubilization within the micelle.
A comparison of the reactions of some ethyl N-Arylcarbamates with those of the corresponding acetanilides. I. Nitration
Authors: Rosevear J , Wilshire JFK
Published: September 2010

The reactions of some ethyl N- arylcarbamates and of the corresponding acetanilides towards 1 equiv. of sodium nitrate in concentrated sulfuric acid at 0-5° have been compared with one another and have been found to exhibit significant differences. Except in the case of the unsubstituted analogues, nitration of the carbamates was found to occur significantly more quickly than that of the acetanilides as shown by ( i ) a representative competitive nitration, and (ii) the fact the carbamates containing a nitro group are nitrated smoothly whereas the corresponding nitroacetanilides are slow to react. On the basis of competitive reactions, it is suggested that this difference in reactivity is due to steric factors.
The Epoxy Lactone Ring of the Coumarin Micromelin: Formation of a New Epimer
Authors: Lamberton JA , Morton TC
Published: September 2010

The five- membered epoxy lactone ring of micromelin opens very readily, without opening of the coumarin ring. Under strongly basic conditions the major product is the methoxy acid isolated by Talapatra et al. Under very mild conditions the five- membered ring may be opened and closed to give either micromelin or isomicromelin [ epimeric at the C4 ( benzylic ) position] according to the nature of the solvent. These studies of isomicromelin confirm the structure previously assigned to micromelin.
Cluster Chemistry. XLI. P-C Bond Cleavage Reactions of Ru3(µ-dppm)(CO)10. Synthesis and Crystal Structure of Ru3[µ3-PPhCH2PPh(C6H4)](CO)9
Authors: Bruce MI , Humphrey PA , Skelton BW , White AH , Williams ML
Published: September 2010

Thermolysis of Ru3(μ- dppm )(CO)10 (1) results in cyclometallation and dephenylation to give the title complex. This complex is also formed, together with Ru3(μ-H)(μ3-PPhCH2PPh2(CO)9, from reaction between (1) with HC5(CO2Me)5.
Chemistry of the Podocarpaceae. LXIX. Further Lignans from te Wood of Dacrydium intermedium
Authors: Cambie RC , Clark GR , Craw PA , Jones TC , Rutledge PS , Woodgate PD
Published: September 2010

Structures and absolute configurations are established for five new lignans isolated from the wood of the New Zealand podocarp Dacrydium intermedium Kirk. X-ray crystallography has been used to confirm the structure of one of the new lignans. Structures for two further inseparable lignans are provisionally assigned. The structure of one of three lignans previously isolated from the wood is revised.
α-Acetylhypoconstictic Acid, a New Depsidone from the Lichen Menegazzia dispora
Authors: Elix JA , Gaul KL , James PW
Published: September 2010

The depsidone, α- acetylhypoconstictic acid (5-acetoxymethyl-1,4- dihydroxy-10-methoxy-8,11-dimethyl-7 H- isobenzofuro [4,5- b][1,4]benzodioxepin-3(1 H),7-dione) (6) has been synthesized and shown to co-occur with atranorin, chloroatranorin, hypostictic acid (3) and hypoconstictic acid (4) in the lichen Menegazzia dispora.The latter depsidone has been isolated and purified for the first time.
Synthesis of the Lichen Dibenzofuran Subdidymic Acid
Authors: Elix JA , Elix JA , Kennedy JM , Kennedy JM
Published: September 2010

The dibenzofuran subdidymic acid (3-hydroxy-7-methoxy-1,9- dipropyldibenzofuran-2-carboxylic acid) has been prepared by unambiguous synthesis.
Kinetics and Stereochemistry of Elimination of Nitrous-Acid From 1-Para-Nitrophenyl-2-Nitroethyl Derivatives
Authors: Norris RK , Wright TA
Published: September 2010

The eliminations of nitrous acid from the compounds (1) and (6) are E2 processes, which proceed with a large primary kinetic isotope effect and with antiperiplanar stereochemistry. The rate of elimination of HNO2 from (1) is intermediate between the rate of elimination of HCl from (4) and HBr from (5). This order of nucleofugality , namely Br- > NO2- > Cl -, results from a more positive entropy of activation for the elimination of nitrous acid. The presence of an α-chlorine, as in compounds (8), (28) and (29), leads to elimination processes which are E1cB-like, with low primary kinetic isotope effects and with lack of stereospecificity.
On the Flat-Band Potential and the Frequency Dispersion of Capacitance and Its Removal in an Normal-Cadmium Telluride in Alkaline Selenide, Polyselenide Photoelectrochemical Cell
Authors: Lyons LE , Young TL
Published: September 2010

When seepage of the
electrolyte between the semiconductor crystal and its insulation was prevented, the equivalent series capacitance CS of an n-CdTe|Se2-, Sen2-,OH-|Pt cell was almost independent of frequency (<2% increase of CS per decade decrease of frequency) in the range 104-2 Hz. Attributing CS wholly to the space-charge capacitance resulted in a linear Mott- Schottky plot and this yielded a flat-band potential of -2.0�0.1 V v . s.c.e . and a built-in potential of 1.08�0.06 V. This was consistent with the observed current-voltage curves in both dark and light. Two conditions under which frequency dispersion was observed were (a) electrolyte seepage and (b) surface damage. The insulating techniques which allowed seepage were similar to those of other workers. The effects of these imperfections on the Mott- Schottky plot are considered. Attempts to extract useful information from frequency dispersion data showed that it is difficult or impossible to obtain a unambiguous equivalent circuit solely on the basis of goodness-of-fit of calculated to observed impedances. The ambiguity can be removed only when sufficient information beyond impedance-frequency data is available. For electrodes with seepage, a model due to Tomkiewicz led to the correct value of the built-in potential.
Synthesis of (±)-Clavularin B
Authors: Urech R
Published: September 2010

(�)- Clavularin B (2b) was prepared from cyclohepta-2,6-dienone (4) via a Michael reaction of
the lithium dienolate anion (5a) with the trimethylsilyl -substituted methyl vinyl ketone (11). The structures of the clavularins A and B were thus unambiguously established as cycloheptenone derivatives (2a) and (2b). The Mukaiyama reaction between the silyl dienol ether (5b) and but-3-en-2-one gave 8-acetyl-4- methylbicyclo[3.2.2]nonan-6-one
(9).
The Crystal-Structure of Silver(I) (2-Carbamoylphenoxy)Acetate
Authors: Mak TCW , Yip WH , Kennard CHL , Smith G , Oreilly EJ
Published: September 2010

The crystal structure of anhydrous silver(I)(2-carbamoylphenoxy)acetate has been determined by X-ray diffraction and refined to a residual of 0.041 for 1532 observed reflections. The complex forms crystal: with space group C2/c and Z4 in a unit cell of dimensions a 20.789(6), b 5.202(1) c 17.318(6)Ǻ, β 105.89(2)°. The structure is based on a centrosymmetric bis-carboxylate bridged dimer [Ag-O 2.228(3), 2.266(3)Ǻ, O-Ag-O 155.8(1)°; Ag…Ag 3.001(1)Ǻ] which is extended into an infinite zigzag polymer through the axial positions via the carbamoyl oxygens of adjacent ligands [Ag-O 2.494(3)Ǻ]. Symmetrical long-rang interactions of phenyl-carbon to silver are also found in the structure [Ag-C 3.094, 3.078(4)Ǻ].
Number- and Weight-Average Molecular Weights for Some Proanthocyanidin Polymers (Condensed Tannins)
Authors: Porter LJ
Published: September 2010

The number-average molecular weights (Mn) and weight-average molecular weights (Mw) for proanthocyanidin polymers (condensed tannins) have been measured by vapour pressure osmometry and low-angle laser light-scattering measurements in methanol. These confirm earlier findings (based on gel permeation chromatography of the peracetate derivatives of these polymers) that they are polydisperse. The results also indicate that the incidence of branching in the polymer chains increases as the average chain length increases.
Synthesis and Properties of Tris[Bis(2-Hydroxy-Ethyl)Dithiocarbamato]Haloditellurium(II) (Halo = Scn-, Br-, I-) and the Crystal-Structure of the Thiocyanato-S Complex, [Te-2((Hoch2ch2)2ncs2)3scn]
Authors: Radha K , Aravamudan G , Rajalakshmi A , Rout GC , Seshasayee M
Published: September 2010

Mixed halo dithiocarbamate complexes of TeII were synthesized for the first time. Complexes of the general formula Te2L3X (X = SCN-, Br- and I-) were obtained from the parent compound TeL2[L = bis (2- hydroxyethyl ) dithiocarbamate ] and potassium thiocyanate or halides in acetic acid medium. Their chemical and physical properties were studied and the crystal
structure of the thiocyanate compound determined. The crystals of the thiocyanate complex are monoclinic, with space group P21/n, a 14.056(3), b 9.599(2), c 22.519(6) Ǻ, β 105.71(2)°, V 2924.8 Ǻ3, Z 4, F(000) 1672, the final R and Rw values being 0.042 and 0.041 respectively for 1209 unique reflections. Many novel aspects were observed in the structure. The two tellurium atoms display entirely different coordinations. One of them, namely, Te(1), has two unequal bidentate dithiocarbamate groups chelated to it in planar-trapezoidal coordination similar to the geometry found in the parent TeL2 complex. It is also linked to Te(2) by a short contact [3.221(3)Ǻ] to complete the fifth coordination. The second tellurium atom Te(2) exhibits trapezoidal four-coordination with an equal bidentate dithiocarbamate group, an S-bonded thiocyanate group, and interestingly with Te(1). The Te(1)-Te(2) axis is inclined with respect to the Te(1)-S(1)-S(2)-S(3)- S(4) plane (trapezoid) by 67.6°.
Applications of 95Mo N.M.R-Spectroscopy. XVI. Structure and Bonding in [Mo(Co)3(η6-Arene)] Complexes From 95Mo,13C and 17O Relaxation-Times
Authors: Brownlee RTC , Oconnor MJ , Shehan BP , Wedd AG
Published: September 2010

Spin-lattice relaxation times (T1) have been measured for the 95Mo, 17O and methine and carbonyl 13C nuclei for a series of [Mo(CO)3(η6-C6H6- nMen)] complexes. In addition to the expected decrease in T1 with increasing molecular volume, the 95Mo and methine 13C data are interpreted in terms of variations in arene -molybdenum bonding. The methine 13C T1 values decrease in the order o- xylene > toluene > p- xylene > m- xylene > mesitylene . The methyl substitution pattern determines the distribution of electron-rich sites on the arene ligand , affecting the molybdenum- arene bond strength and the barrier to arene rotation. These observations support an earlier proposal that downfield 95Mo chemical shifts are associated with increased molybdenum- arene bond strength. 95Mo T1 values are unaffected by the rotational barriers, since they depend only on molecular tumbling perpendicular to the pseudo C3v symmetry axis. While these T1 values decrease as the number of methyl groups increases, an effect due to increasing molecular volume, the order of 95Mo T1 for the xylene complexes is opposite to that of the 13C T1, due to a reduction in the electric field gradient at the 95Mo nucleus. 95Mo quadrupole coupling constants for the series are 1.2�0.2 MHz. The 17O T1 values have also been measured for this series. They are considerably longer, and quadrupole coupling constants smaller (0.87�0.07 MHz), than those of other metallocarbonyls , indicating a significant increase in metal- ligand dπ-pπ - back bonding in the present system. A correlation between carbonyl force constants and 17O quadrupole coupling constants is presented.
An Investigation of Adduct Complexes of M(S2CNEt2)2(Co)2 (M=Mo,W) by 95Mo and 183W N.M.R-Spectroscopy
Authors: Young CG , Enemark JH
Published: September 2010

The seven-coordinate adducts M(S2CNEt2)2(CO)2L and [M(S2CNEt2)2(CO)2]2-μ-L (M = Mo, W;L below), derived from the 16-electron complexes M(S2CNEt2)2(CO)2, have been investigated by 95Mo and 183W n.m.r. spectroscopy. The molybdenum and tungsten adducts exhibit resonances in the regions from 310 to -430 and from -465.5 to -1500 ppm , respectively. All the resonances are shielded relative to those of the M(S2CNEt2)2(CO)2 precursors. The dependence of the nuclear shielding on L is as follows. For M = Mo: NH2NHSO2C6H4Me < Cl - < OPPh3 < μ- pyrazine < pyridine < NH2NHCOPh < NH2NMe2 < μ-NH2NHMe < μ-NH2NH2 < μ-NH2CH2CH2NH2 < NH3
< N3- < F- < AsPh3 < PPh3 < SbPh3 < PPh2Et < PPh2Me < PMe3 < P( OPh )3 < P( OEt )3 < P( OMe )3 < CO. For M = W: NH2NHCOPh < AsPh3 < Ph2PCH2PPh2 < PPh3 < PPh2Et < Ph2PCH2CH2PPh2 < PPh2Me < PMe3 < P( OPh )3 < P( OEt )3 < P( OMe )3
< CO. The OPPh3, halide and nitrogen-donor ligand adducts participate in a dynamic equilibrium with Mo(S2CNEt2)2(CO)2 on the n.m.r . time scale. The remaining adducts do not exhibit such behaviour. The chemical shifts of both the molybdenum and tungsten adducts are correlated with the π- acceptor ability of the ligand , L, and the stereochemistry of the adducts. A linear relationship between the chemical shifts of analogous molybdenum and tungsten complexes is observed; the equation of the line is δ(183W) = 1.46δ(95Mo)-857.5.
Amide Tricobaltcarbon Clusters With Multiple Redox Centers
Authors: Robinson BH , Simpson J , Trounson ME
Published: September 2010

The complexes FcNHC (O)CCo3(CO)9 ( Fc = ferrocenyl ) (3) and Fc ( alaOMe )C(O)CCo3(CO)9 (ala = alanine ) (5) have been synthesized from the +C(O)CCo3(CO)9 cation and FcNH2 or Fc ( alaOMe )H respectively. Derivatives FcNHC (O)CCo3(CO)6[P( OPh )3]3 (4) and Fc ( alaOMe )C(O)CCo3(CO)6[P( OPh )3]3 (6) are also described. Analysis of the spectroscopic and redox behaviour shows that the amide linkage acts as a -I, -M substituent group to Fc and the Co3C unit acts as a-I, +M group. Unlike complexes where these redox centres are directly linked, electronic effects are not transmitted between Co3C and Fc . Oxidation at the ferrocene centre and reduction at the Co3C centre in (3) and (5) is chemically reversible whereas oxidation of the amino acid moiety is irreversible; oxidation of the cluster takes place in (4) and (6) but no intervalence charge transfer is observed.
Isodidymic Acid, a New Dibenzofuran From the Lichen .Cladonia didyma
Authors: Chester DO , Elix JA , Kennedy JM
Published: September 2010

The dibenzofuran isodidymic acid (3-hydroxy-7-methoxy-9-pentyl-1-propyl-dibenzofuran-2-carboxylic acid) has been synthesized and shown to co-occur with barbatic acid, subdidymic acid and condidymic acid in Cladonia didyma.
Electrolyte Molar Volumes at 273-373-K in Propylene Carbonate, N-Methylformamide, Formamide and Methanol: Their Relation to Solvent Compressibility. Ion Association Constants in Acetonitrile at 298-K
Authors: Bottomley GA , Bremers MT
Published: September 2010

Measurements have been made on several electrolytes of their apparent molar volumes at 25°C by dilatometry and typically from 0°C to 125°C by expansimetry in propylene carbonate, N- methylformamide, formamide, and methanol. The electrolyte limiting apparent molar volumes are shown to be linearly related to the temperature dependent isothermal compressibility in these solvents, as in water. Ion-pair equilibrium associated constants have been determined by volumetric means for NH4SCN, KSCN and ten other electrolytes in acetonitrile at 25°C and similarly for MgSO4 in water at 25°C. Less extensive apparent molar volume studies in water 0 to 160°C for high charge species and in liquid sulfur dioxide at 25° are also reported.
Experiments Directed Towards the Synthesis of Anthracyclinones. XII. Preparation of a Substituted Isobenzofuran From an Anthradifuran
Authors: Boddy IK , Cambie RC , Rutledge PS , Woodgate PD
Published: September 2010

The anthradifuran (4) has been converted into the substituted isobenzofuran (29), a potential intermediate for the synthesis of anthracyclinones from anthraquinones . The sequence involves the intermediates (19), (24) and (34). Selective openings of one of the furan rings of the anthradifuran (4) have been investigated.
Synthesis of 3-(4′-Methoxyphenyl)-2,2,4,4-Tetramethylpentane and Some Cyclic Analogs
Authors: Collins DJ , Jacobs HA
Published: September 2010

Reaction of 1-methoxy-2-methyl-1-trimethylsilyloxyprop-1-ene (8) with 1-acetoxy-1-(4′-methoxyphenyl)-2,2-dimethylpropane (7b) in the presence of zinc iodide gave 84% of methyl 3-(4′methoxyphenyl)-2,2,4,4- tetramethylpentanoate (9a), which was reduced with lithium aluminium hydride to 3-(4′-methoxyphenyl)-2,2,4,4-tetramethylpentan-1-ol(12a). Hydride reduction of the derived tosylate (12b) afforded 3-(4′-methoxyphenyl )-2,2,4,4-tetramethylpentane (5b) which upon demethylation yielded the corresponding phenol (10a). In an analogous manner, 1-acetoxy-1-(4′-methoxyphenyl)-2-methylpropane (7d) was converted into 3- (4′-hydroxyphenyl)-2,2,4-trimethylpentane (10b). By a similar reaction sequence, 6-methoxy-2,2-dimethyl-3,4- dihydronaphthalen-1(2H)-one (14) was transformed into 6-hydroxy-2,2- dimethyl-1-(1′,1′-dimethylethyl)-1,2,3,4-tetrahydronaphthalene (16b). Hydrolysis of the ester (9a) and cyclization of the resulting carboxylic acid (19) by treatment with methanesulfonic acid at 20° for 18 h afforded 3-(1′, 1′-dimethylethyl)-6-methoxy-2,2-dimethyl-2,3-dihydro-1H-inden-1-one (20). Clemmensen reduction of this followed by demethylation yielded 1-(1′,1′-dimethylethyl)-2,2-dimethyl-2,3-dihydro-1H-inden-5-ol (21b). Attempts to oxidize the phenols (10a), (10b), (16b) and (21b) to the corresponding quinone methides by conventional methods failed.