bluuebunny/crossref_metadata_2025 huggingface dataset:
The chemistry of small‐ring compounds. Part 38. The transient existence of 1‐(p‐anisyl)cyclopropyl cation
Authors: van der Vecht J. R. , Dirks R. J. , Steinberg H. , de Boer Th. J.
Published: September 2010

A cyclopropyl cation, stabilized by a p‐anisyl group

Anisyl = methoxyphenyl.

, turns out to be an intermediate in the alcoholysis of 1‐(p‐anisyl)cyclopropyl halides. In other reactions with nucleophiles substitution products are also formed predominantly without ring rupture.

The influence of the solvent, nature of nucleophiles and added salts on reaction rates and product distributions support an SN1 type mechanism.
Polyisocyanides 5. Synthesis and polymerization of carbylhistidine and carbylhistamine
Authors: van der Eijk J. M. , Nolte R. J. M. , Drenth W.
Published: September 2010

Polymer anchored imidazole functions were obtained by polymerization of carbylhistidine and carbylhistamine. These isocyanides were synthesized from L‐histidine and histamine, respectively. In order to obtain the former isocyanide in optically active form, it was necessary to work at low basicity and to prevent temperatures higher than ambient. Polymerization occurred with 1 mol % nickel chloride and a small amount of trifluoroacetic acid in methanol. The poly(carbylhistidine) showed no optical activity. The apparent pKa of the imidazole function in poly(carbylhistamine) has decreased to 5.2 ± 0.1 compared with free imidazole (7.2), whereas it rises to 9.4 ± 0.2 in poly(carbylhistidine).
The application of levulinic acid as protective group to the synthesis of tetradecaribonucleotide U‐A‐U‐A‐U‐A‐U‐A‐U‐A‐U‐A‐U‐A via the modified phosphotriester method
Authors: van Boom J. H. , Burgers P. M. J.
Published: September 2010

Acylation on the 5î‐position of 2î‐O‐methoxytetrahydropyranyl ribonucleosides la (B=U) and 2a (B=Aan) with levulinic acid, followed by phosphorylation of the 3î‐hydroxy function with the monofunctional phosphorylating agent 2,2,2‐trichloroethyl 2‐chlorophenyl phosphoro‐chloridate (3), afforded the fully‐protected mononucleotides 4a and 5a, respectively, in reasonable yields. The latter compounds were key‐intermediates in the synthesis of fully‐protected tetradecaribonucleotide 15a. The preparation of tetradecamer 15a was achieved by using two specific deblocking procedures, i.e. (a) zinc in pyridine/2,4,6‐triisopropylbenzenesulfonic acid to cleave the 2,2,2‐trichloroethyl group and (b) hydrazine in pyridine/acetic acid for the rapid and selective removal of the levulinyl group. Deblocking of the 2‐chlorophenyl groups from 15a was successfully accomplished by the action of fluoride ion. Attention is directed to anomalous reactions occurring with the use of this deblocking reagent.
Acidity and reactivity of some supported molybdenum oxide catalysts
Authors: Ragaini Vittorio , Matarrese Giovanni , Giordano Nicola , Bart Jan C. J.
Published: September 2010

The acidity of MoO3·γ‐Al2O3, MoO3·SiO2, MoO3·SiO2·Al2O3 systems has been determined by measuring the heat of immersion in pyridine; a non‐monotonic variation with the MoO3 percentage has been observed in the range from 0 ‐ 25 wt% MoO3. The extremes are: 4, 8*, 15 and 25* wt % MoO3 on γ‐A2O3; 3,4*, 7, 13*, 16 and 23* wt % MoO3 on SiO2; 1*, 2, 8* and 25 wt % MoO3 on SiO2·Al2O3, where asterisks denote maxima. For the MoO3·Al2O3 and MoO3·SiO2 systems the activity for double‐bond isomerization of 1‐butene has been measured in the temperature range of 200‐245° and apparent activation energies ΔEa have been derived. As a function of the composition, ΔEa shows a minimum for the 14 wt% MoO3·SiO2, a weak maximum (16 wt%) and a steep minimum (8 wt%) for MoO3·Al2O3 catalysts. The selectivity of the isomerisation reaction has been discussed in terms of surface structure and acidity. It is concluded that the formation of various catalytic species rather than the variation of acidity or the deposition of carbonaceous residues accounts for the selectivity of MoO3·Al2O3 and MoO3·SiO2 catalysts towards isomerization of 1‐butene to cis‐ and trans‐2‐butene and therefore for the variation of the apparent activation energy with composition.
The structure of the condensation product of methyl cyanoacetate and 2,4‐dimethoxy‐6‐chloro‐l,3,5‐triazine
Authors: Weber A. J. M. , Huysmans W. G. B. , Mijs W. J. , Bovée W. M. M. J. , Smidt J. , Vriend J.
Published: September 2010

From NMR and IR measurements it appeared that the title compound occurs in solution in two tautomeric forms, a predominant NH, and an enolised ester form. Both forms are in rapid equilibrium. The structure (I) expected for this type of condensation does not occur. A second exchange process involves breaking of an intramolecular H‐bond combined with rotations about the triazinyl side chain bond.
Synthesis of racemic and optically active codeine and morphine via the N‐formylnordihydrothebainones: (Chemistry of opium alkaloids, part X)
Authors: Beyerman H. C. , van Berkel J. , Lie T. S. , Maat L. , Wessels J. C. M. , Bosman H. H. , Buurman E. , Bijsterveld E. J. M. , Sinnige H. J. M.
Published: September 2010

Starting from 3,4,5‐trihydroxybenzoic acid (gallic acid), racemic 1‐(3,5‐dibenzyloxy‐4‐methoxybenzyl)‐1,2,3,4‐tetrahydro‐6‐methoxyisoquinoline (3, Scheme) was synthesized. Resolution with (‐)‐(S)‐malic acid yielded (+)‐(R)‐3. By a Birch reduction, followed by N‐formylation, and by acid‐catalysed cyclization, we obtained racemic and optically active N‐formyl‐2‐hydroxynordihydrothebainone (6). 6 Was selectively converted into N‐formyl‐2‐(1‐phenyltetrazol‐5‐yloxy)nordihydrothebainone (7). Hydrogenolysis of (‐)‐7 and of racemic 7 yielded (‐)‐N‐formylnordihydrothebainone (8) and racemic 8, respectively. Previously we had converted the N‐formyl derivative (8) in various ways into dihydrothebainone. The conversion into (‐)‐codeine and (‐)‐morphine is known.
Steric effects in alkylpyrimidines
Authors: van der Plas H. C. , Koudijs A.
Published: September 2010

Treatment of solutions of 4,6‐dimethylpyrimidine and 4,6‐di‐t‐butylpyrimidine in acid with aliphatic acids (RCO2H) in the presence of silver nitrate and ammonium peroxydisulfate gave the 2‐R‐4,6‐dimethyl‐ and 2‐R‐4,6‐di‐t‐butylpyrimidines (R = C2H5, i‐C3H7, t‐C4H9). Ths pKa values of these compounds were measured. It was found that 2,4,6‐tri‐t‐butylpyrimidine is a weaker base than expected by about 1.6 pKa units. Oxidation of 2‐isopropyl‐4,6‐di‐t‐butylpyrimidine with permaleic anhydride gives 2‐isopropyl‐4,6‐di‐t‐butylpyrimidine N‐oxide. Under the same conditions 2,4,6‐tri‐t‐butylpyrimidine could not be converted into the corresponding N‐oxide.
Asymmetric reductions by a chiral pyridine‐dinucleotide model
Authors: van Ramesdonk H. J. , Verhoeven J. W. , Pandit U. K. , de Boer Th. J.
Published: September 2010

The reduction of two activated carbonyl compounds by a chirally substituted 1,4‐dihydronicotinamide system is described. Although the chiral centre is far removed from the reaction centre, a rather high (up to 27%) asymmetric induction is observed. This degree of asymmetric induction is discussed in relation to the ‐ independently documented ‐ differential substrate accessibility of the two diastereotopic faces of the nicotinamide ring.
Topochemistry. Part XL. 1The crystal structures of trans‐1,2‐dibenzoyl‐ and 1,2‐di‐p‐toluylethylene
Authors: Bart J. C. J. , Schmidt G. M. J.
Published: September 2010

The crystal structures of the two title compounds (I and II, respectively) have been solved from partial three‐dimensional data by means of SEARCH, and refined by a full‐matrix least‐squares programme with anisotropic temperature factors of all but the hydrogen atoms to r = 0.042, 0.031, R = 0.078, 0.075.

The bond lengths and angles (e.s.d. 0.01 Å, 0.3°) are consistent internally and between the two molecules, as well as with similar values in related molecules.

The molecules are centrosymmetric and have adopted the cisoid conformation of the C=C‐C=O group. The benzene rings, and the CC(O)C and CCCC systems are planar, with dihedral angles between these groups of 12.0° (I), 9.7° (II) and 12.6° (I), 4.4° (II).

Upon irradiation trans‐1,2‐dibenzoylethylene undergoes a single‐crystal‐single‐crystal transformation to the cis‐isomer.
Convenient methods for the preparation of di(1‐alkynyl) sulfides, sulfoxides and sulfones, and application of the sulfoxides and sulfones in the formation of novel heterocyclic systems
Authors: Verboom W. , Schoufs M. , Meijer J. , Verkruijsse H. D. , Brandsma L.
Published: September 2010

Di(1‐alkynyl) sulfides and the corresponding sulfoxides are obtained in high yields from lithium alkynides and sulfur dichloride or thionyl chloride, respectively. The di(1‐alkynyl) sulfoxides and also the corresponding sulfones (prepared by oxidation of di(1‐alkynyl) sulfides with m‐chloroperbenzoic acid) react very rapidly with disodium sulfide, selenide or telluride to form six‐membered heterocyclic compounds.
Force field calculations on some t‐butyl substituted cyclohexane compounds
Authors: van De Graaf B. , Baas J. M. A. , Wepster B. M.
Published: September 2010

The results are reported of empirical force field calculations on conformers of t‐butylcyclohexane, cis‐ and trans‐1,4‐di‐t‐butylcyclohexane and trans‐1,2‐di‐t‐butylcyclohexane using the force fields of Allinger et al. (AFF) and of Schleyer et al. (SFF). Comparisons of energy differences and geometric data with experimental values show that both force fields yield useful results; SFF gives the better correlation. The A value of the t‐butyl group is calculated to be 4.7 kcal mol−1 (19.7 kJ mol−1). Cis‐1,4‐di‐t‐butylcyclohexane and trans‐1,2‐di‐t‐butylcyclohexane are predicted to exist as conformational mixtures. The concept of additivity in the prediction of strain energies is discussed.
Mechanism of the catalytic inhibition of hydrocarbon autoxidation by secondary amines and nitroxides
Authors: Bolsman T. A. B. M. , Blok A. P. , Frijns J. H. G.
Published: September 2010

A study has been made of the mechanism of the catalytic inhibition of autoxidation of hydrocarbons at 130°C by secondary amines and derivatives thereof (hydroxylamines and nitroxides). From the effect of hydrocarbon structure on the inhibition and from the various reactions of possible intermediates of the catalytic cycle, it is concluded that alkyl and alkylperoxyl radicals are scavenged alternately. Reaction of an alkyl radical with a nitroxide produces an O‐alkylated hydroxylamine. In the case of tertiary alkyl radicals this hydroxylamine decomposes thermally ‐ via transfer of the β‐hydrogen from the alkyl group to the nitroxide moiety ‐ into olefin and hydroxylamine. The hydroxylamine is subsequently oxidized back to the nitroxide by alkylperoxyl radicals. Kinetic data on the individual steps of the cycle are in accord with the observed inhibiting effect.
Organocuprate induced allylic versus propargylic 1,3‐substitution in sulfinates and sulfonates derived from 3‐hydroxy‐1‐penten‐4‐ynes. Improved synthesis of a precursor for the presumed sex attractant of Acanthoscelides obtectus
Authors: Kleijn H. , Westmijze H. , Kruithof K. , Vermeer P.
Published: September 2010

The sulfinates (E)‐R1‐C≡C‐C(R2, CH=CHR3)‐OS(O)Me (1) have been treated with [R4CuBr]MgX·LiBr (4) in tetrahydrofuran. The ratio allylic versus propargylic 1,3‐substitution in 1, leading to R1‐C≡C‐CR2=CH‐CHR3R4 (2, Z/E ≥ 86/14) and (E)‐R1R4C=C=CR2‐CH=CHR3 (3) respectively, depends on the size of the substituents R1 and R3. As could be concluded from the reaction of (E)‐1 (R1=R2=H, R3= ‐CH(OEt)2) and of the corresponding methanesulfonate (E)‐5 with the heterocuprate [n‐C8H17CuBr]MgBr·LiBr, the ratio 2/3 is also influenced by the nature of the leaving group. A very high regioselectivity has been found if (E)‐5 was reacted with the homocuprate (n‐C8H17)2CuMgBr·LiBr instead of the heterocuprate. The latter reaction is part of an attractive route to the presumed sex attractant of the Male Dried Bean Beetle (Acanthoscelides obtectus).
Conversion of 1‐alkyne‐1‐thiolates and ‐selenolates into thioketene and selenoketene precursors. Preparation of bis(trimethylsilyl)selenoketene, the first stable selenoketene
Authors: Sukhai Ramesh S. , Brandsma Lambert
Published: September 2010

Lithium 1‐alkynethiolates and ‐selenolates RC≡CXLi (X = S, Se) have been converted with allyl bromide and with 1‐bromo‐2‐butyne into the compounds H2C=CH‐CH2‐X‐C≡C‐R and CH3C≡C‐CH2‐XC≡C‐R (R = t‐C4H9, Me3Si; X = S, Se), respectively. Upon heating, only the sulfides H2C=CH‐CH2‐S‐C≡C‐R gave isolable thioketenes by [3,3]‐sigmatropic rearrangement. The analogous selenoketene and the thioketene from the rearrangement of Me3Si‐C≡C‐X‐CH2CCH3 are unstable.

In the reaction of CH3C≡C‐SeSiMe3 and t‐C4H9C≡C‐SeSiMe3 with diethylamine, giving the selenoamides C2H5C(Se)NEt2 and t‐C4H9CH2C(Se)NEt2, the selenoketenes CH3CH=C=Se and t‐C4H9CH=C=Se are the presumed intermediates. Pure bis(trimethylsilyl)selenoketene [Me3Si]2C=C=Se (7) was obtained in 80% yield from the reaction of Me3SiC≡C‐SeLi and Me3SiCl at low temperatures.
Nature of the chemical reaction path
Authors: Fukui Kenichi
Published: September 2010

The importance of orbital concepts in experimental chemistry is stressed in connection with interpreting the nature of chemical reaction paths. The outstanding role of particular orbital interactions is recognized in various elaborate theoretical calculations. Mathematical formulation of the “intrinsic reaction coordinate” is decisively helpful in a quantitative, nonempirical understanding of the characteristic feature of reaction paths and also provides applications to “reaction ergodography” and to the calculation of absolute rates.
Helicenes: A striking temperature dependence in a chemically induced asymmetric photosynthesis
Authors: Vanest J.‐M. , Martin R. H.
Published: September 2010

A very high diastereoselectivity is observed when the (‐)‐menthyl ester I is photocyclised at −78°C: (+)98:(‐)2. The ratio is nearly reversed at 80°C: (+)20:(‐)80.
The reversible photochemistry of 1,2‐di‐(2‐naphthyl)cyclopentene
Authors: Wismontski‐Knittel T. , Kaganowitch M. , Seger G. , Fischer E.
Published: September 2010

The title compound 1 undergoes photocyclization to 4a,4b‐dihydrophenanthrene (DHP) derivatives corresponding to two of the three possible conformers 1A, 1B, 1C. The ratio DHPA/DHPB varies with the wavelength of the photoactive light. At lower temperatures only DHPB is formed. DHPA is virtually stable at 25°C, while DHPB decays with a half‐life of 5 × 10−4 s. Both DHP's are oxidized with iodine to the corresponding phenanthrene derivatives. DHPA is strongly fluorescent, it is photo‐oxidized at 436 nm with oxygen even at −150°C. The photoreversion DHPA→1A is inefficient at 25°C and sharply attenuated on cooling. Two modifications of DHPA were observed. This is as expected according to calculations by the CFF‐SCF‐PI‐CI method, which was also used to calculate the geometries and energies of the conformers and the DHP's.
A formalism for the classification and design of organic reactions. I. The class of (− +)nreactions
Authors: Arens J.F.
Published: September 2010

A coding system for the classification of organic reactions is proposed. The reacting atoms are considered as points on a cycle and the bonds between these points are indicated by 1, 2, 3 or 0 meaning a single, double, triple or no bond respectively.

These bonds change during the reaction. The present paper deals with reactions where the number of points is even and where the reaction changes the bonds in a regular fashion, alternatively diminishing or increasing the bond order with one unit.

This class of reactions is denoted as reactions with operator (−+)n. Many reactions of great synthetic utility belong to this class.
The reductive animation of 4‐tert‐butylcyclohexanone with an NADH model
Authors: de Nie‐Sarink M.J. , Pandit U.K.
Published: September 2010

4‐tert‐Butylcyclohexanone undergoes reductive amination to a mixture of isomeric 1‐pyrrolidino‐4‐tert‐butylcyclohexanes (3a,b) upon reduction with Hantzsch ester (2), in the presence of pyrrolidine and the corresponding perchlorate. Under standardized conditions (10 equiv. of pyrrolidine, 1 equiv. of pyrrolidine perchlorate), only 75% of the product (3a,b) is formed via reduction by the Hantzsch ester. The remaining 25% is produced in a process which involves a hydride transfer from either the pyrrolidine (secondary amine) or the enamine system, generated as an intermediate in the reaction to the corresponding iminium salt. The stereochemistry of the Hantzsch ester reduction has been investigated by the use of 4,4‐dideutero‐Hantzsch ester (7).
A quantitative study on the relationship between structure and behavioural activity of peptides related to ACTH
Authors: Kelder J. , Greven H.M.
Published: September 2010

A series of peptides related to ACTH and MSH with behavioural potencies determined in a pole‐jumping test on rats has been analysed using a modified Free‐Wilson method (Fujita‐Ban analysis). A stepwise multiple linear regression programme was used for the calculation of the individual contributions of the sub‐units to the overall activity. In general a good agreement between calculated and observed potencies was found. This result shows that the use of a model based on independent contributions of the amino acid residues in the peptide chain to the overall biological activity was justified. Inspection of the few exceptions to this rule led to valuable suggestions about spatial interactions at the receptor level.
Photoreactions of ortho‐vinyl triphenylethylenes I. The photochemistry of 1,2‐diphenyl‐1‐(2‐vinylphenyl)ethylene
Authors: Kulyk M. Sindler , Laarhoven W.H.
Published: September 2010

Irradiation of the title compound (9) causes two types of photoreactions. endo‐1,6‐Diphenyl‐2,3‐benzobicyclo[3.1.0]hex‐2‐ene**, endo‐(13), is a primary photoproduct resulting from an intramolecular [4 + 2]cycloaddition; it is partially converted into exo‐(13). [2 + 2]Cycloaddition does not occur. This results fits well into the general scheme previously proposed for the photochemical behaviour of o‐vinylstilbenes.

The other photoproducts (14‐17) are formed via electrocyclisation reactions occurring in the divinyl‐benzene moiety and in a cis‐stilbene moiety of 9.
Synthesis of phospholipids via phosphotriester intermediates
Authors: Lammers J.G. , van Boom J.H.
Published: September 2010

A new phospholipid synthesis has been developed. Phosphorylation of a 1,2 diacylglycerol with the monofunctional reagent R1R2POCl (R1 and R2 being phosphate‐protecting groups) provides a phosphotriester in 70–90% yield. Removal of one protecting group affords a phosphodiester, which is condensed with the required alcohol to a second phosphotriester (70–75% yield, based on the first triester). Subsequently, the other phosphate‐protecting group and, if present, groups protecting other functionalities are split off. Of the protecting groups investigated, optimal results were obtained with R1 = NHC6H5 and R2 = OCH2CCl3. In this way, phosphatidylethanolamine, phosphatidylglycerol, N,N‐dimethylphosphatidylethanolamine and phosphatidic acid were prepared.
Absorption spectra and reaction kinetics of the radical anion, radical cation and OH adduct(s) of 3,5‐dinitroanisole studied by pulse radiolysis
Authors: Tamminga Johannes J. , van den Ende Cornelis A. M. , Warman John M. , Hummel Andries
Published: September 2010

Pulse radiolysis of an aqueous solution of 3,5‐dinitroanisole (dNA) containing 0.1 mol dm−3 isopropanol results in the formation of the radical anion of dNA by attachment of solvated electrons with a rate constant of 4.2 × 1010 dm3 mol−1 s−1 and by reaction of dNA with the isopropanol radical, (CH3)2COH, with a rate constant of 2.5 × 109 dm3 mol−1 s−1. The absorption spectrum of dNA− is characterised by a maximum at approximately 275 nm (ϵ,≈︁14 × 103 dm3 mol−1 cm−1) with shoulders at 300 nm and 410 nm. The extinction coefficient is less than 100 dm3 mol−1 cm−1 in the wavelength region 500 nm to 600 nm. The anion decays by a second order process the rate of which decreases with increasing pH.

Reaction of OH radicals with dNA in an aqueous solution occurs with a rate constant of 4 × 109 dm3 mol−1 s−1 and results in an absorption in the visible region. The absorption can be separated into two components with maxima at 470 nm and 515 nm on the basis of differing decay kinetics at different wavelengths. The absorption with γmax = 470 nm has an additional band which increases into the infra red and is assigned to a complex between the OH radical and the π‐electron system of dNA. The absorption with γmax = 515 nm is assigned to a combination of the four possible cyclohexadienyl type radicals which can result from σ‐bond formation between OH and a ring carbon atom.

An absorption with γmax = 480 nm, found on pulse irradiation of a deaerated solution of dNA in cyclohexane, is attributed to the radical cation of dNA. The extinction coefficient of dNA+ is estimated to be 6.0 + 0.6 × 103 dm3 mol−1 cm−1.
Structure and conformation of heterocycles. X. On 1,4,5,8‐tetraazadecalins
Authors: Fuchs Benzion , Ellencweig Aviyakar
Published: September 2010

A synthetic, structural and conformational study of 1,4,5,8‐tetraazadecalin (3) and several of its new, substituted derivatives was performed. Mass‐spectrometric and NMR‐spectroscopic data were taken to indicate a trans‐fused double chair in most cases. These findings, juxtaposed to the notorious elusiveness of trans‐1,4,5,8‐tetraoxadecalin (2) were rationalized in terms of a “reverse anomeric effect”. Substituent effects were also assessed: substituents in the two angular positions or on all four nitrogens preclude trans fusion in favour of the isomeric cis‐ and/or biimidazolidin‐2‐yl structures. The cis‐geometry also prevails in systems were it is imposed by bridging substituents.
Synthesis and acid‐ and base‐catalyzed reactions of hexobarbital 1′,2′‐epoxide and heptabarbital 1′,2′‐epoxide
Authors: Bakker B. H. , van der Gen A. , Vermeulen N. P. E. , Breimer D. D.
Published: September 2010

The synthesis of 1′,2′‐epoxides of hexobarbital (1a) and heptabarbital (1b) is described. Epoxide2a(from1a) consists of a mixture of diastereoisomersIandII. Only isomerIIis able to undergo base‐catalysed cyclization with formation of furopyrimidine3a. Epoxide2b(from1b) likewise affords furopyrimidine3b. The chemical behaviour of3aand3bindicates the occurrence of a ring‐opened keto tautomer. Upon treatment with acid, epoxides2a,bundergo cleavage with formation of C5‐alkyl‐substituted barbituric acids7a,b, thus explaining the absence of 1′,2′‐dihydroxy compounds among the metabolites of barbiturates1aand1b.
Reactions of carbon nucleophiles with 4‐phenyl‐ and 4‐tert‐butyl‐5‐halogenopyrimidines. On the occurrence of an SRN1 mechanism
Authors: Oostveen E. A. , van der Plas H. C.
Published: September 2010

Reaction of 5‐X‐4‐phenylpyrimidine (X = Br, Cl) with the enolate anions of acetone and acetophenone in liquid ammonia yields 5‐acetonyl‐ and 5‐phenacyl‐4‐phenylpyrimidine, respectively. It is shown that these reactions proceed via an SRN1 mechanism. Reaction of 5‐X‐4‐phenylpyrimidine (X = Br, Cl) with the enolate anion of pinacolone gives besides SRN1 substitution, addition of the anion to the N(1)‐C(6)‐azomethine bond. On treatment of 5‐X‐4‐tert‐butylpyrimidine with the enolate anions of acetone, acetophenone or pinacolone, substitution products are formed in very low yields. Addition of potassium to the liquid ammonia or irradiation with near ultraviolet light, however, increases the yields of 5‐substituted 4‐tert‐butylpyrimidine derivatives considerably.
Anomalous effects in measurements of rotational barriers in formamidinium ions. Influence of solvent, counter‐ion and concentration
Authors: Staps R. J. F. M. , Scheeren J. W. , Pijpers F. W. , Nivard R. J. F.
Published: September 2010

Chemical exchange studies on the tetramethylformamidinium ion lead to anomalous values for the Arrhenius parameters of internal rotation when apolar solvents, high concentrations and nucleophilic anions are used. The deviations cannot be ascribed to ion‐pairing, and might be due to covalent bonding.
Synthesis of the 5′‐triphosphate of a trimer containing 2′‐5′‐internucleotide linked riboadenosines
Authors: den Hartog J. A. J. , Doornbos J. , Crea R. , van Boom J. H.
Published: September 2010

Starting from two properly protected building blocks derived from adenosine and two effective phosphorylating agents, a fully protected intermediate containing two 2′‐5′‐internucleotide phosphotriester bonds and one functionalized 5′‐phosphotriester group was prepared. Selective deblocking of one protective group from the 5′‐phosphotriester function, followed by reaction with pyrophosphoric acid and subsequent removal of all protecting groups, afforded the 5′‐triphosphate of a 2′‐5′‐linked trimer of riboadenosine.
A simple synthesis of N,N‐dialkyl‐3‐alken‐1‐yn‐1‐amines
Authors: Verboom W. , Everhardus R. H. , Bos H. J. T. , Brandsma L.
Published: September 2010

3‐Alken‐1‐yn‐1‐amines R‐CH=CH‐C≡C‐NR′2, 9 (R = H, Me, R′ = alkyl) have been prepared in good yields by treatment of the Mannich products MeO‐CH(R)‐C≡C‐CH2‐NR′2 ‐ obtained from propargylic ethers MeO‐CH(R)‐C≡C‐H, paraformaldehyde and dialkylamines R′2NH ‐ with strong bases under polar aprotic conditions.
The role of tetraalkylammonium salts in the electro‐reduction of ketones III. Pinacolization and asymmetric induction
Authors: van Tilborg W. J. M. , Smit C. J.
Published: September 2010

Several alkyl aryl ketones have been electro‐reduced in an aprotic medium in the presence of tetraalkylammonium conducting salts. Quantitative yields of the corresponding pinacols have been obtained, except in cases where steric crowding in the starting ketone hampers the pinacolization. When chiral conducting salts are used considerable levels of enantiomeric excess in the (RS + SR) fractions of the pinacols are achieved.
Synthesis of fragments of human β‐lipotropin, βh‐LPH. Part I. The synthesis of β‐LPH‐(61‐76) and β‐LPH‐(61‐77), i.e. α‐ and γ‐endorphin, respectively
Authors: Bijl W.A.A.J. , van Nispen J.W. , Greven H.M.
Published: September 2010

The synthesis of β‐LPH‐(61–76) and β‐LPH‐(61–77) [i.e. α‐ and γ‐endorphin, respectively] by means of the fragment condensation approach is described.

Several of the fragments leading to these two endorphins were also obtained as pure, free peptides.
Interpretation of vicinal proton‐proton coupling constants by a generalized Karplus relation. Conformational analysis of the exocyclic C4′‐C5′ bond in nucleosides and nucleotides: Preliminary Communication
Authors: Haasnoot Cornelis A. G. , de Leeuw Frank A. A. M. , de Leeuw Harry P. M. , Altona Cornelis
Published: September 2010

New values for 3JHH along the C4′‐C5′ bond in nucleosides and nuclsotides are proposed.
Infrarotspektroskopischer Nachweis des Amins HgNH2OH·HgO, das bei der Bildungsreaktion der Millonschen Base in Form des Monohydrates auftritt
Authors: Weber Richard
Published: September 2010

Die Bildungsreaktion der Millonschen Base wird infrarotspektroskopisch untersucht. Es gelingt, die Reaktion auf der Stufe des Imin‐Monohydrates abzufangen. Durch Trocknung desselben ist es möglich, zum Amin zu gelangen. Das Amin‐Spektrum wird mitgeteilt. Auch das Diammin konnte hergestellt und dessen Spektrum aufgenommen werden.
An efficient method for the trimethylsilylation of tertiary alcohols
Authors: Visser R. G. , Bos H. J. T. , Brandsma L.
Published: September 2010

Tertiary acetylenic alcohols have been transformed into the O‐trimethylsilyl derivatives with trimethylsilyl chloride and triethylamine, using catalytic amounts of dimethyl sulfoxide, hexamethylphosphoric triamide, imidazole, or 1,5‐diazabicyclo[5.4.0]undec‐5‐ene. Saturated tertiary alcohols can be trimethylsilylated in the same way.
Regiospecific functionalisation of unsaturated compounds via their dilithio derivatives: Part 1: Reaction of dilithio compounds of 1‐alkynes with epoxides, benzyl halides and trimethylchlorosilane
Authors: Hommes H. , Verkruijsse H. D. , Brandsma L.
Published: September 2010

Acetylenes HCCCH2R (R = H, alkyl) have been converted with good yields into their derivatives HCCCH(E)R (E = CH2CHR′OH, CH2Ph, SiMe3) by reaction of the dilithio compound LiCCCH(Li)R with epoxides OC2H3R′ ( R′ = H, Ph), benzyl chloride and trimethylchlorosilane (TMSCI), respectivily.
Synthesis of methyl (E,Z,Z)‐2(or 4 or 6),9,12‐octadecatrienoate and methyl (E,Z,Z)‐2(or 6 or 8),11,14‐eicosatrienoate
Authors: Klok R. , Möhlmann W. M. M. , van der Wolf L. , Pabon H. J. J.
Published: September 2010

For studies into the relationship between their physical properties and chemical structure, several polyunsaturated fatty acids related to (Z,Z,Z)‐6,9,12‐octadecatrienoic acid and (Z,Z,Z)‐8,11,14‐eicosatrienoic acid were synthesized.

Methyl (E,Z,Z)‐2,11,14‐eicosatrienoate and methyl (E,Z,Z)‐2,9,12‐octadecatrienoate were prepared by E‐stereoselective coupling of (methoxycarbonylmethylene)triphenylphosphorane with (Z,Z)‐9,12‐octadecadienal and (Z,Z)‐7,10‐hexadecadienal respectively.

The synthesis of methyl (E,Z,Z)‐4,9,12‐octadecatrienoate started from 2,7‐octadiyn‐1‐ol which was reduced with lithium aluminium hydride. The (E)‐2‐octen‐7‐yn‐1‐ol thus obtained was coupled with 1‐bromo‐2‐octyne to give (E)‐2‐hexadecene‐7,10‐diyn‐ 1‐ol. This was converted into 1‐chloro‐(E)‐2‐hexadecene‐7,10‐diyne, which via malonic ester synthesis yielded (E)‐4‐octadecene‐9,12‐diynoic acid. Stereospecific hydrogenation and esterification finally afforded the desired compound, from which methyl (E,Z,Z)‐6,11,14‐eicosatrienoate was obtained by chain elongation.

Methyl (E,Z,Z)‐6,9,12‐octadecatrienoate was synthesized from 1,4‐dichloro‐(E)‐2‐butene which was converted into (E)‐4‐octen‐7‐ynoic‐7‐ynoic acid. Coupling the latter with 1‐bromo‐2‐octyne, esterification and reduction yielded (E‐4‐hexadecene‐7,10‐diyn‐ 1‐ol. Conversion into the corresponding chloro compound and stereospecific hydrogenation yielded 1‐chloro‐(E,Z,Z)‐4,7,1 O‐hexadecatriene. Malonic ester synthesis finally afforded the desired compound.

The synthesis of methyl (E,Z,Z)‐8,11,14‐eicosatrienoate started from 2‐octyne‐1,8‐diol which was reduced with lithium aluminium hydride; the resulting (E)‐octene‐1,8‐diol was converted into 1,8‐dichloro‐(E)‐2‐octene. The latter was coupled with 1,4‐decadiyne to give 1‐chloro‐(E)‐6‐octadecene‐9,12‐diyne, which was hydrogenated stereospecifically. Malonic ester synthesis finally completed the synthesis.
A study of orientation effects of electronegative substituents on vicinal carbon‐proton spin‐spin coupling constants and the correlation of the latter with proton‐proton coupling constants in the individual rotamers of 13CH3‐C(X)1H‐C(Y)1H2 fragments
Authors: Spoormaker Tom , de Bie Marius J. A.
Published: September 2010

Orientation effects of electronegative substituents on vicinal carbon‐proton coupling constants are studied in 1,2‐disubstituted propanes and are found to resemble those on vicinal proton‐proton coupling constants. Known relations for the orientation effect of substituents on synclinal proton‐proton coupling constants can be modified so that they yield reasonable values for synclinal carbon‐proton coupling constants.
Empirical force field calculations VI: Exploration of reaction paths for the interconversion of conformers. Application to the interconversion of the cyclohexane conformers
Authors: van de Graaf B. , Baas J. M. A. , van Veen A.
Published: September 2010

A method is described for the calculation of reaction paths for the interconversion of conformers by forcing the internal rotation around one or more single bonds. The implementation of the method in a general computer program for molecular mechanics is discussed. It is shown that forcing the average of two or three torsion angles has distinct advantages. Results of calculations on the interconversion of the cyclohexane conformers are presented as an example.
Formation of (η3‐methallyl) and (η4‐butadiene) ligands from (η1‐2‐buten‐1‐yl) coordinated to group IVB metals
Authors: Blenkers J. , de Liefde Meijer H. J. , Teuben J. H.
Published: September 2010

The synthesis and some properties of the novel triallyl compounds Cp*M(CH2CHCHCH3)3 (Cp*=η5‐C5(CH3)5; M=Ti, Zr or Hf ) and the butadiene‐methallyl compounds Cp*M(η4‐butadiene) (η3‐methallyl) therefrom are reported. The compounds are very reactive towards carbon monoxide and other small molecules.
Empirical force field calculations VII. Rotation of the tert‐butyl groups on the chair conformers of tert‐butylcyclohexane, 9‐tert‐butylbicyclo[3.3.1]nonane and cis‐1,2‐di‐tert‐butylcyclohexane
Authors: Baas J. M. A. , van de Graaf B. , van Veen A. , Wepster B. M.
Published: September 2010

Empirical force field calculations indicate the existence of two chair conformers of cis‐1,2‐di‐tert‐butylcyclohexane. The energy difference amounts to 4.82 kJ mol−1 using the Engler force field. Reaction paths for the interconversion of these conformers have been explored by means of the forced rotation of the tert‐butyl groups. Six transition states have been found in a complicated scheme. The barriers to rotation of both tert‐butyl groups are compared with those calculated for an axial and an equatorial tert‐butyl group on the chair conformation of cyclohexane and on position 9 of bicycle[3.3.1]nonane.
Ketonic complexes of acetylacetone and ethyl acetoacetate with divalent transition metals
Authors: Driessen W. L. , Everstijn P. L. A.
Published: September 2010

Several new coordination compounds are reported with 2,4‐pentanedione (acacH) and ethyl 3‐oxobutanoate (etaaH) as the neutral bidentate oxygen donor ligands, viz. [M(acacH)3]‐ (InCl4)2 and [M(etaaH)3](InCl4)2 where M is Mg(II), Mn(II), Fe(II), Co(II), Ni(II) and Zn(II). In the complexes the ligands are present in their ketonic form. The metal ions are surrounded octahedrally by six oxygen atoms.
A frontier orbital description of the reaction of singlet oxygen with simple aromatic systems
Authors: van den Heuvel C. J. M. , Verhoeven J. W. , de Boer Th. J.
Published: September 2010

Frontier molecular orbital theory has been applied to the [4 + 2]‐cycloaddition of singlet oxygen, to mono‐ and dimethylnaphthalenes and to a number of other polycyclic aromatic compounds. Semilogarithmic plots of rate constants versus second order perturbation energies are found to be linear. The good correlations are due partly to the fact that singlet oxygen is such a small dienophile.
Chemistry of electron‐rich conjugated polyenes VI. A comparative study of the rates and mechanism of [4 + 2]‐cyclo‐additions between alkoxy‐1,3‐butadienes and β,β‐dicyanostyrenes
Authors: Broekhuis A. A. , Scheeren J. W. , Nivard R. J. F.
Published: September 2010

The kinetics of [4 + 2] cycloadditions in several solvents have been studied for reactions between ring‐substituted β,β‐dicyanostyrenes (2a–j) and a series of methoxybutadienes (1a–e), differing in electron‐donating properties, conformational preference and polarity. All reactions studied gave linear Hammett plots with positive p values when log k/k0 values were plotted against σ+ substituent constants. Solvent effects appeared to be small.

The results have been discussed on the basis of differences in the HOMO‐LUMO interaction and in conformational factors for differing pairs of reactants. In this way more detailed insight has been obtained into variations in the nature (olefin‐like or product‐like) and polarity of the transition state of these reactions.
The crystal structure of copper(II) (R,S)‐1‐amino‐2‐propanol chloride
Authors: Nieuwpoort G. , de Kok A. J. , Romers C.
Published: September 2010

Copper(II) (R,S)‐1‐amino‐2‐propanol chloride, Cu(C3NOH9),Cl2, is monoclinic. The lattice constants at 22°C are a = 8.050(5), b = 10.930(6), c = 8.120(6) Å, β = 92.20(6)°, Z = 4 and μ(MoKα) = 37.95 cm−1.

Extinctions 0k0 with k odd indicate the space group P21, but weak reflections h0l with l odd demonstrate that the symmetry almost corresponds to P21/c. The structure was solved by Patterson methods. Least‐squares refinement in P21/c was unsatisfactory but refinement in P21 resulted in a final R value of 0.038 for 2192 reflections, 1772 of which have intensities greater than 2σ(I). The structure is disordered and shows three conformations of the ligand, i.e. the structure contains as major form, (58%), ligands A and Ā and as minor form, (42%), ligands B and C. In all cases the copper atoms are coordinated octahedrally by four chlorine atoms, one nitrogen and one oxygen atom. Two chlorine atoms are bound at 2.273(1) Å and 2.247(1) Å and two at 2.993(1) Å and 3.181(1) Å.
The chemistry of small ring compounds. Part 43. Synthesis of 1‐substituted cyclopropyl sulfides
Authors: Jorritsma R. , Steinberg H. , de Boer Th. J.
Published: September 2010

1‐Hydroxy‐ and 1‐halocyclopropyl sulfides can be conveniently prepared starting from cyclopropanone. Cyclopropyl sulfides with halogen or a dimethylsulfonium group in the α‐position can be transformed into 1‐substituted cyclopropyl sulfides with a variety of nucleophiles. This means that the usual difficulties encountered with nucleophilic substitution at three‐membered rings ‐ i.e. low rates and ring opening — are largely removed by the presence of an alkylthio group at the same ring carbon atom as the leaving group.
Photo‐induced electron transfer from NADH and other 1,4‐dihydronicotinamides to methyl viologen
Authors: Martens F. M. , Verhoeven J. W.
Published: September 2010

The photo‐induced oxidation of NADH and its model compound, 1‐benzyl‐1,4–dihydronicotinamide (BNAH), by N,N′‐dimethyl‐4,4′‐bipyridinium dichloride (methyl viologen: MV+ +) was studied in homogeneous and in micellar solution. In the overall, slightly endoergonic, reaction: NADH + 2 MV+ + + hv → NAD+ + 2 MV +• + H+ the dihydropyridines lose a hydride equivalent via a stepwise e,H+,e sequence in which only the initial one‐electron transfer requires photostimulation. It is shown that the singlet‐excited state of the dihydropyridine is the photoreactive intermediate in this initial electron transfer process and that the overall quantum yield depends critically on the ratio of the rates for ionic dissociation and back‐electron transfer in the encounter complex between this excited state and MV+ + molecules. This ratio can be influenced dramatically by changing the solvent medium. In aqueous solution (for NADH) and especially in anionic micellar solution (for BNAH) strong ground state association between MV+ + and the dihydropyridines occurs. Evidence for this association is provided by the appearance of a long‐wavelength charge transfer absorption, as well as by the large deviations from a Stern‐Volmer behaviour observed in the quenching of the dihydropyridine fluorescence by MV+ +. The ground state complexation appears to hamper ionic dissociation of the excited complex. This is evident from the low quantum yield for photooxidation of such systems, upon excitation of the dihydropyridine chromophore (365 nm), and the complete absence of such oxidation upon their excitation within the charge transfer absorption (546 nm). The data obtained are shown to allow for a complete thermodynamic analysis of the Gibbs free‐energy changes involved in loss of a hydride equivalent from a 1,4‐dihydropyridine via a stepwise e,H+,e mechanism. The consequences of this analysis for the mechanism of reactions in which 1,4‐dihydropyridines transfer a hydride equivalent to various substrates under thermal conditions are discussed.
Fluorination of 2‐bromo‐4,5‐dimethylphenol with xenon difluoride
Authors: Koudstaal H. , Olieman C.
Published: September 2010

Fluorination of 2‐bromo‐4,5‐dimethylphenol (1) with xenon difluoride, using boron trifluoride etherate as catalyst, gave 2‐bromo‐4,5‐dimethyl‐4‐fluorocyclohexa‐2,5‐dienone (2), 2‐bromo‐3,4‐dimethyl‐6‐fluorophenol (3) and 6‐bromo‐3,4‐dimethyl‐2‐fluorophenol (4). The products were isolated by means of preparative reverse‐phase HPLC and identified by 1H and 13C NMR spectroscopy.
A convenient, stereospecific synthesis of racemic juvenile hormones and some of their analogues via vinylcuprates
Authors: Kleijn H. , Westmijze H. , Meijer J. , Vermeer P.
Published: September 2010

This paper describes a stereospecific synthesis of nine 2E,6E, 10(Z)‐trienyl esters R1R2CCH(CH2)2CR3CH(CH2)2CR4CHCO2Me (1a‐i) and their selective conversion into the corresponding epoxides magnified image (7a‐i), including the natural occurring hormones JHI‐III. The trienyl system of 1 has been reached stereospecifically by allowing specifically substituted vinylcuprates, [R1R2CCHCuY]⊖, to react with 4‐iodo‐1‐butyne, followed by conversion of the formed enynes R1R2CCH(CH2)2CCH (3) into new cuprates of the type thus [R1R2CCH(CH2)2CR3CHCuY]⊖. These cuprates furnish, upon reaction with 4‐iodo‐l‐butyne, the dienynes R1R2CCH(CH2)2CR3CH(CH2)2CCH (5). From 5, vinylcuprates [R1R2CCH(CH2)2CR3CH(CH2)2CR4CHCuY]⊖ have been obtained which, upon reaction with carbon dioxide followed by methylation, gave compounds 1. For the preparation of the vinylcuprates from the 1‐alkynes we generally used a new alkylcopper(I) species of the type R3Cu2MgX. The epoxidation of 1 into 7 was performed using a literature procedure.
The mechanism of the photocyclization of 1,4‐diarylbutenynes into aryl‐substituted aromatics. The influence of amines and oxygen
Authors: van Arendonk R. J. F. M. , de Violet P. H. Fornier , Laarhoven W. H.
Published: September 2010

The formation of a 1,2,4‐cyclohexatriene derivative (cf. 7) from the singlet‐excitedcis‐butenyne is thought to be the primary reaction step in the photocyclization of 1,4‐diarylbutenynes. This very reactive intermediate can yield the end‐product along various pathways: (i) directly via a [1,5] hydrogen shift; (ii) via radical intermediates, formed either by acceptance of a hydrogen atom from the solvent (e.g.benzene, hexane) or by release of a hydrogen atom in the presence of oxygen; (iii) via ionic intermediates, formed either by acceptance of a proton (e.g.from methanol) or by release of a proton in the presence of amines. The rates of the cyclization are approximately equal for various butenynes. Differences in product quantum yields are mainly due to differences in the rates of the ring‐opening reaction of the cyclic allene. Using laser flash photolysis two transients of the cyclization could be observed. The effect of amines on the transients is described.
The reaction of 2‐butynedinitrile with 2,3,4,5‐tetramethylfuran
Authors: Hall R. H. , Harkema S. , den Hertog H. J. , van Hummel G. J. , Reinhoudt D. N.
Published: September 2010

2‐Butynedinitrile reacts by (2 + 4)‐cycloaddition with one or two equivalents of 2,3,4,5‐tetramethylfuran to give 1,4,5,6‐tetramethyl‐7‐oxabicyclo[2.2.1]hepta‐2,5‐diene‐2,3‐dicarbonitrile (1) and 1α,4α,4aα, 5β,8β,8aα‐hexahydro‐1,2,3,4,5,6,7,8‐octamethyl‐1,4:5,8‐diepoxy‐naphthalene‐4a,8a‐dicarbonitrile (5), respectively. The presence of aluminium(III) chloride has no effect on the reactions, unlike the corresponding reaction with the analogous thiophene. On irradiation, 1 is converted into 2,4,6,7‐tetramethyl‐3‐oxatetracyclo[3.2.0.02,7.04,6]heptane‐1,5‐dicarbonitrile (2) in good yield. The structure of 5 has been determined by a single‐crystal X‐ray analysis.
Studies on polypeptides. XXXV. Synthesis of a partially protected heptapeptide, corresponding to the sequence 14–20 of bovine pancreatic ribonuclease
Authors: Hoogerhout P. , Schattenkerk Cecile , Kerling K. E. T.
Published: September 2010

The partially protected heptapeptide, Boc—Asp(OtBu)—Ser—Ser‐Thr‐Ser‐Ala‐Ala‐OH, corresponding to the sequence 14‐20 of bovine pancreatic ribonuclease, was prepared by a combination of solid‐phase synthesis using Nα‐(9‐fluorenylmethoxycarbonyl) amino acids and synthesis in solution by the active ester method. The overall yield was 38%.
Synthesis of oligoribonucleotides with sequences identical to the nucleation region of Tobacco Mosaic Virus RNA: Preparation of AAG, AAGAAG and AAGAAGUUG via phosphotriester methods
Authors: den Hartog J. A. J. , Wille G. , van Boom J. H.
Published: September 2010

The synthesis of the oligoribonucleotides AAG (23), AAGAAG (24) and AAGAAGUUG (25), corresponding to fragments of the nucleation region of Tobacco Mosaic Virus RNA, is described. The assemblage of the oligomers 23–25 was effected using a phosphotriester method which was based on the use of the monofunctional phosphorylating agents 2,2,2‐trichloroethyl 2‐chlorophenyl phosphorochloridate (7) and the analogous 2,2,2‐tribromoethyl 2‐chloro‐4‐tert‐butylphenyl phosphorochloridate (8). The levulinyl function, which was introduced into the monomeric building blocks 1 (see Scheme 1) by an improved procedure, was used for the protection of the 5′‐hydroxyl group of phosphotriester intermediates. Deblocking of the fully protected oligomers 15f, 17g and 19h with fluoride ions, followed by ammonia and acid treatment, afforded the desired derivatives AAG, AAGAAG and AAGAAGUUG, respectively, in good yields.
Synthesis of three new compounds structurally related to damascone and ionone
Authors: Witteveen Jan G. , van der Weerdt Anton J. A.
Published: September 2010

1‐(3,6,6‐Trimethyl‐1,3‐cyclohexadien‐1‐yl)‐2‐buten‐1‐one (1), a β‐damascenone isomer, was synthesized from 3,6,6‐trimethyl‐2‐cyclohexenone (14). This starting ketone 14 was obtained in good yield from 3‐methyl‐2‐butanone (11) and 3‐buten‐2‐one (12). Ethynylation of 14 with 3‐butyn‐2‐ol afforded acetylenic diol 20. Acid‐catalyzed rearrangement of 20 yielded
1‐(3,6,6‐Trimethyl‐1‐cyclohexen‐1‐yl)‐2‐buten‐1‐one (2), a β‐damascone isomer, was prepared from 1 by hydrogenation. Ketone 2 is shown to be identical to a naturally occurring compound found in fusel oil.
4‐(3,6,6‐Trimethyl‐1‐cyclohexen‐1‐yl)‐3‐buten‐2‐one (3), a β‐ionone isomer, was obtained by condensation of 3,6,6‐trimethyl‐1‐cyclohexenecarboxaldehyde (29) with acetone. Aldehyde (29) was synthesized from 2,2,5‐trimethylcyclohexanone (16) by reaction of its tosylhydrazone 28 with n‐butyllithium and DMF.
The compounds 1–3, 17–21 and 25–29 are new. 1.
Prenylation of methoxyhydroquinone in aqueous acid solution and an alternative synthesis of precocene II
Authors: Uchiyama M. , Overeem J. C.
Published: September 2010

The acid‐catalyzed condensation of methoxyhydroquinone with 2‐methyl‐3‐buten‐2‐ol leads to 2‐methoxy‐5‐(3‐methyl‐2‐butenyl)hydroquinone (4) and 2‐(1,1‐dimethylallyl)‐5‐methoxy‐hydroquinone (7). Compound 4 can easily be converted into precocene II (1, R  Me).
Acid‐catalysed isomerisation of epoxides to allylic alcohols
Authors: van Zon A. , Huis R.
Published: September 2010

The acid‐catalysed isomerisation of epoxides containing tertiary ring carbon atoms results in the selective formation of the corresponding allylic alcohols if the reaction is carried out in methylene chloride or chloroform in the presence of small quantities of sulfuric acid (< 10 mmol/l) or methanesulfonic acid (< 100 mmol/l). The zero‐order kinetics of the isomerisation have been rationalised by a mechanism in which a rapidly and quantitatively formed epoxide‐acid intermediate slowly decomposes into allylic alcohol and acid.