bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the occurrence of the anrorc‐mechanism and a dimroth rearrangement in reactions of 4‐halogenopyrimidines with lithium isopropylamide
Authors: van Der Plas H. C. , Koudijs A. 
Published: September 2010

AbstractIn the reaction of 6‐bromo‐4‐phenylpyrimidine (1) with lithium isopropylamide at − 75°, the open‐chain product N′‐(2‐cyano‐1‐phenyl‐1‐vinylene)‐N‐isopropyl‐formamidine (5) is obtained. On standing, compound 5 isomerises slowly into 6‐imino‐4‐phenyl‐1‐isopropyl‐1,2‐dihydropyrimidine (6). On reaction of 1 with lithium isopropylamide at 20°, 4‐phenyl‐6‐isopropylaminopyrimidine (7) was formed. Evidence has been presented that 7 is formed by a complicated series of reactions involving an ANRORC‐mechanism (1 → 5 → 6) and a subsequent Dimroth rearrangement (6 → 9 → 10 → 7).
Vinyl orthoformates and vinyl acetals II: The reactions of alkenyl orthoesters and dialkenyloxyalkyl carboxylates with carboxylic acids
Authors: van Melick J. E. W. , Scheeren J. W. , Nivard R. J. F. 
Published: September 2010

AbstractSeveral new alkenyl orthoesters have been synthesized by dehydrohalogenation of the corresponding β‐chloroalkyl orthoesters with various bases. With one equivalent of a carboxylic acid these compounds are converted into dialkenyloxyalkyl carboxylates in good yields. Dependent upon their composition, the latter products, give with another equivalent of a carboxylic acid either predominantly alkenyl esters and acylals, or alkenyl esters, carboxylic anhydrides and carbonyl derivatives. The synthetic applications have been investigated and a possible mechanism for these reactions is given.
A synthesis of N‐phthaloyl amino acids and amino acid esters under mild conditions
Authors: Hoogwater D.A. , Reinhoudt D.N. , Lie T.S. , Gunneweg J.J. , Beyerman H.C. 
Published: September 2010

AbstractThe racemization‐free synthesis of N‐phthaloyl amino acids (Pht‐amino acids) from amino acid esters, by using o‐methoxycarbonylbenzoyl chloride in anhydrous media, is described. The N‐phthaloyl amino acids and esters from proteins were obtained in high yields.Three N‐phthaloyl amino acids were synthesized for the first time: N‐Pht‐LTrp, N‐Pht‐S‐Bzl‐LCys and N‐Pht‐Nim‐Bzl‐LHis.In the case of some sterically hindered amino acids, LIle and α‐amino‐isobutyric acid, the intermediate N‐(o‐methoxycarbonylbenzoyl) amino acid derivative could be isolated.
Photoaddition of aromatic ketones to some arylacetylenes; Formation of α,β‐unsaturated ketones and aldehydes
Authors: Polman H. , Mosterd A. , Bos H.J.T. 
Published: September 2010

AbstractPhotoaddition of aromatic ketones to 1‐alkyl‐2‐phenylacetylenes RCCC6H5 (R = CH3, C2H5) generally affords, via an oxete derivative, α,β‐unsaturated ketones Ar2CC(C6H5)COR in good or moderate yield.With monosubstituted arylacetylenes Ar′CCH α,β‐unsaturated aldehydes Ar2CC(Ar′)CHO are formed.In the reactions with 9‐xanthenone partial dehydrocyclization of the adducts occurs.
Synthesis of thiepen and thiocin derivatives via ring enlargement
Authors: Reinhoudt D.N. , Kouwenhoven C.G. 
Published: September 2010

AbstractA general method has been developed for the synthesis of two novel classes of heterocyclic compounds, 2,3‐(or 2,7)‐dihydrothiepins and 2,3‐dihydro‐8H‐thiocins. It comprises the cycloaddition of enamine derivatives of tetrahydro‐thiophen‐3‐ones or 4‐thiacyclohexanone to activated acetylenes, e.g. dimethyl acetylenedicarboxylate, yielding bicyclic adducts, which upon thermal ring opening of the cyclobutene moiety afford the thiepin and thiocin derivatives.The enamine group in these cyclic dienamines can be hydrolysed to give stabilized enols and/or their tautomeric ketones.Peracid oxidation of the sulfur atom in the dihydrothiepins or dihydro‐2H‐thiocins produces the corresponding 1‐oxides or 1,1‐dioxides.
Synthesis of thiahydrindanones and thiadecalones by Dieckmann cyclization: The stereochemistry of thiolate anion addition to cyclohexenes
Authors: van Bruijnsvoort A. , de Waard E. R. , van Bruijnsvoort‐Meray J. L. , Huisman H. O. 
Published: September 2010

AbstractThe synthesis of trans‐3‐thiadecal‐1‐one (5) and cis‐3‐thiahydrindan‐1‐one (12) by Dieckmann cyclization (DC) is described. Anions of mercapto‐esters are shown to add to activated cyclohexenes in a trans diaxial fashion in kinetically controlled Michael additions (MA). An explanation is presented for the retro‐MA of cis‐1‐(2î‐ethoxycarbonylethylthio)‐2‐ethoxycarbonylcyclohexane (10) under DC‐conditions.
Pyrazoles and imidazoles as ligands. Part xviii: Neutral and anionic pyrazole coordinated to Cu(I) and Ag(I)
Authors: Okkersen H. , Groeneveld W. L. , Reedijk J. 
Published: September 2010

AbstractA few compounds having the general formula M(L)+2 X− are reported, in which M(I) = Cu or Ag, X− = BF−4, NO−3, Cl−, Br−, and L stands for pyrazole, 3(5)‐methylpyrazole and 4‐nitropyrazole. The compounds are formed by reaction of MX and L in acidic medium. Infrared spectra of the compounds are consistent with linear cations ML+2 and uncoordinated anions.Apart from the above compounds, a different class of compounds is formed in less protic media. These compounds are salt like and have the formula M+L−, with M+ = Cu+ and Ag+ and L = pyrazole, 4‐iodopyrazole, 4‐bromopyrazole, 4‐ethylpyrazole, 4‐nitropyrazole and 3(5)‐methylpyrazole.Infrared spectra, mass spectra, X‐ray powder diagrams and solubility studies indicate that these compounds are at least trimeric and possibly polymeric with bridging pyrazolate anions between the metal ions.
Chemistry of α‐nitrosulfones. Part I: Sulfinate elimination from α‐sulfonylnitroalkane anion radicals
Authors: Zeilstra J. J. , Engberts Jan B. F. N. 
Published: September 2010

AbstractElectron transfer reactions to 2‐nitropropyl p‐tolyl sulfone (1) using different electron donors, are described. Using potassium 2‐propylnitronate as the electron donor, the product formation is proposed to occur via a free radical chain process involving rapid elimination of p‐toluenesulfinate anion from the anion radical derived from 1. When the carbon atom connecting the nitro and sulfonyl groups bears hydrogen, the corresponding α‐sulfonyl nitronate is formed as the only product under comparable conditions. Treatment of l‐iodo‐l‐nitro‐l‐(p‐tolylsulfonyl) propane with potassium 2‐propylnitronate in ethanol affords the potassium salt of l‐nitro‐l‐(p‐tolylsulfonyl) propane, 2,3‐dimethyl‐2,3‐dinitrobutane and iodine. Possible mechanisms for the formation of these products are briefly discussed.
On the occurrence of the SN(ANRORC)‐mechanism in the reaction of 2‐bromo‐4‐phenylpyrimidine with potassium amide in liquid ammonia
Authors: Kroon A. P. , van der Plas H. C. 
Published: September 2010

AbstractOn amination of 2‐bromo‐4‐phenylpyrimidine with potassium amide, 2‐amino‐4‐phenylpyrimidine, β‐amino‐β‐phenylacrylonitrile and 4‐amino‐l‐cyano‐2‐phenyl‐l‐aza‐1,3‐butadiene are formed.2‐Bromo‐4‐phenyl‐[l,3‐15N]‐pyrimidine has been prepared and found to give on amination 2‐amino‐4‐phenylpyrimidine. which contains the original15N mainly in theexocyclicamino group. This is explained by a mechanism, involving an initial Addition of the Nucleophile to position 6, a subsequent Ring‐Opening by fission of the N(1)‐C(6) bond and Ring‐Closure (SN(ANRORC)‐mechanism).
Consecutive reactions in the thermal high pressure hydrogenolysis of tetralin and indan: Part II
Authors: Penninger J. M. L. , Slotboom H. W. 
Published: September 2010

AbstractReaction models were derived by analogue simulation, to describe the course of the reaction in the hydrogenolysis of tetralin and indan up to high conversion levels.The side chain cracking of n‐butylbenzene results mainly in styrene, ethyl‐benzene and toluene; n‐propylbenzene preferentially forms styrene and ethyl‐benzene, while l‐methylindan undergoes demethylation and α ring‐opening almost exclusively at the methyl substituted C‐atom.Mechanisms proceeding via benzylic radicals, are proposed for the side chain cracking.
The ESCA‐method as an additional tool for structure elucidation: Investigations of compounds derived from active methylene compounds and carbon disulfide
Authors: Kolind‐Andersen H. , Dalgaard L. , Jensen L. , Lawesson S.‐O. 
Published: September 2010

AbstractThe structures of various compounds derived from active methylene compounds and carbon disulfide have been determined by ESCA‐measurements of the binding energy of the 2p1/2 and 2p3/2 electrons of the two sulfur atoms in the compounds. The choices between alternative structures agree with statements from other methods of molecular spectroscopy (IR, NMR).
The tris(biuretato)cobaltate(III) ion: The crystal structure of potassium tris(biuretato)cobaltate(III) hydrate
Authors: Birker P. J. M. W. L. , Smits J. M. M. , Bour J. J. , Beurskens P. T. 
Published: September 2010

AbstractThe structure of the octahedral N6‐coordinated potassium tris(biuretato)‐cobaltate(III) hydrate, K3Co(HNCONHCONH)3. xH2O (x = 6.38) was determined by X‐ray analysis. The crystals are triclinic, space group \documentclass{article}\pagestyle{empty}\begin{document}$ \bar 1 $\end{document}, with unit cell dimensions a = 9.296, b = 11.168, c = 11.631 Å, α = 93.76°, β = 112.71°, γ = 74.57° and two formula units per cell. 3275 non‐zero reflections were measured with an automatic diffractometer. The structure was refined by full matrix least‐squares methods to a conventional R‐value of 0.05. The cobalt is in nearly regular octahedral coordination with an average Co‐N distance of 1.916 Å. The slightly puckered biuretato ligands are somewhat bent out of the plane formed by four coordinating nitrogen atoms and the cobalt atom.
Hydride transfer reactions: V. Kinetics and mechanism of the reduction of hydroxyallyl and tetrahydrofuryl ions with isobutane in HF‐SbF5 and HF‐BF3
Authors: Brouwer D. M. , Kiffen A. A. 
Published: September 2010

AbstractProtonated mesityl oxide (1) and 3‐penten‐2‐one (3), and the 2,5,5‐trimethyltetrahydrofuryl (5) and 2,5‐dimethyltetrahydrofuryl (7) ions react with isobutane to give the corresponding saturated ketones and tert‐butyl ion. The reactions are very much faster in 9:1 HF‐SbF5 than in HF‐BF3; ions 1 and 5 react far more rapidly than 3 and 7, respectively. These “ionic hydrogenations” are concluded to take place via transfer of hydride ion from isobutane to the alkylcarbonium carbon of intermediate dications (C,O‐diprotonated alkenones). This mechanism also accounts for the findings that 5 and 7 are hydrogenated much more rapidly than 1 and 3, respectively, in spite of the fact that the former ions are thermo‐dynamically far more stable than the latter. The reversibility of these reactions has been demonstrated in the case of cation 5.
Studies on vitamin D and related compounds XXIII: The structure of bischolestadienol isomers
Authors: Boomsma F. , Jacobs H. J. C. , Havinga E. , van der Gen A. 
Published: September 2010

AbstractThe photodimerization product of 7‐dehydrocholesterol was found to consist of three isomers to which structures 4b, 5b and 6b are assigned.
Chemistry of α‐nitrosulfones. Part III. A new convenient synthesis of α‐nitrosulfones
Authors: Zeilstra J.J. , Engberts Jan B. F. N. 
Published: September 2010

AbstractA number of x‐nitrosulfones have been prepared in reasonable yields by reaction of p‐toluenesulfonyl iodide with metal nitronates. The reaction is a free radical chain process rather than a nucleophilic displacement of iodide by the nitranion. A possible reaction path involving the intermediacy of x‐iodonitroalkane radical anions is indicated. The synthetic procedure could be simplified by adding iodine to a solution of sodium p‐toluenesulfinate and the appropriate potassium nitronate in DMF. The mass spectra of several x‐nitrosulfones are briefly discussed.
Chemistry of acetylenic ethers 104 Thermal rearrangement of 1‐alkynyl 2‐alkynyl sulfides in the presence of dialkylamines or dialkylphosphines. A new type of thio‐claisen rearrangement
Authors: Meijer J. , Vermeer P. , Bos H.J.T. , Brandsma L. 
Published: September 2010

Abstract1‐Alkynyl 2‐alkynyl sulfides, R1CCS‐CH2CCR2, 1, rearrange at room temperature (if R2 = H) or upon heating (if R2 = alkyl). The thioketenes, H2CCC(R2)‐C(R1)CS, 2, presumed to be formed can be trapped by secondary amines, or‐in some cases‐by dialkylphosphines. Depending upon the nature of the substituents R1 and R2 and upon the solvent, allenic thioamides, H2CCC(R2)‐CH(R1)C(S)NR32, 3, conjugated dienic thioamides, H2CCHC(R2)C(R1)C(S)NR32, 4, thiophene derivatives, 5, or mixtures of these types of compounds, are formed.
Intramolecular catalysis in cis‐diethyl 2‐carboxyvinylphosphonate hydrolysis
Authors: van der Holst J. P. J. , van Hooidonk C. , Kienhuis H. 
Published: September 2010

AbstractThe hydrolysis of the title compound proceeds very fast in weakly acidic aqueous media by a stepwise release of both ethyl ester groups via phosphorus‐oxygen bond fission. The reactions are about 106 times faster than that for the release of one ethyl group of the corresponding trans‐isomer. The observed kinetics are consistent with a mechanism involving intramolecular catalysis by the undissociated carboxyl group.
A regiospecific N‐substitution of asymmetrically alkylated imidazoles: The preparation of 1,5‐dialkyl‐ and 1,2,5‐trialkylimidazoles
Authors: Godefroi E. F. , Mentjens J. H. F. M. 
Published: September 2010

AbstractAbstract. A method for regiospecific N‐alkylation of 4 (or 5)‐methylimidazoles (1a‐c) to 1,5‐disubstituted and 1,2,5‐trisubstituted derivatives has been elaborated. The process consists of the regiospecific N‐acetylation of 1a‐c to give isomerically pure 3a‐c; these are quaternized and deacetylated to 5a‐j. When simplified to a one‐pot synthesis, yields up to 40% of N‐substituted products are realized.
Electron transfer reactions between trivalent phosphorus compounds and activated ketones
Authors: Boekestein G. , Voncken W. G. , Jansen E. H. J. M. , Buck H. M. 
Published: September 2010

AbstractThe present paper presents a mechanism for the reaction between trivalent phosphorus compounds ‐ P(OR)3, R = alkyl and P {N(CH3)2}3 ‐ and molecules with activated carbonyl groups such as α‐diketones, o‐quinones and α,β‐unsaturated ketones. It appeared from ESR measurements that intermediate radicals which originate in a high concentration are converted into oxyphosphoranes. In the case of P(OR)3 an intramolecular shift could be established as a side reaction. Furthermore a number of interesting spin adducts are formed between phosphinium radicals and the scavenger 2‐methyl‐2‐nitrosopropane.
Synthesis of 1‐alkenyl derivatives of isothiocyanates, dithiocarbamates and thioureas
Authors: Hoff S. , Blok A. P. 
Published: September 2010

AbstractReductive cleavage of the sp3 carbon‐sulfur bond in alkyl‐or aryl‐substituted 2‐mercapto‐or 2‐amino‐6H‐1,3‐thiazines with sodium in liquid ammonia affords almost quantitative yields of the sodium salts of 1‐alkenyl‐dithiocarbamates and ‐thioureas, respectively. The dithiocarbamates can be converted into 1‐alkenyl isothiocyanates by reaction with chloroformates and subsequent pyrolysis to give overall yields of 54‐88%. Cis‐trans isomerization of the 1‐alkenyl isothiocyanates can only be achieved by irradiation.
Preparation and ESR of phosphorus spiro compounds. Part III
Authors: Rothuis R. , Freide J. J. H. M. Font , van Dijk J. M. F. , Buck H. M. 
Published: September 2010

AbstractThe synthesis of 2,2′‐biphenylenediphenylphosphonium, 2,2′‐biphenylenephenylbenzylphosphonium and 2,2′‐biphenylenephenyl(p‐nitrophenyl)phosphonium salts is described. The related phosphoranyl radicals I, IV and V, generated by electrochemical reduction, are measured by ESR spectroscopy. A similar procedure is followed for the radicals II and III; related phosphonium compounds are described in the literature.The small values of the phosphorus doublet splitting constants are an indication for a tetrahedron (T) like configuration of the phosphorus. The odd electron is delocalized in the aromatic ligands and the five 3‐dorbitals of the phosphorus.It is shown that the spin‐ and odd electron density distribution depends on the electron affinity of the aryl ligands. This is confirmed by quantum chemical calculations.
Conformational analysis of cis‐ and trans‐1,2‐di‐tert‐butylcyclohexane and some homomorphs
Authors: van de Graaf B. , van Bekkum H. , van Koningsveld H. , Sinnema A. , van Veen A. , Wepster B. M. , van Wijk A. M. 
Published: September 2010

AbstractSpectroscopic data of cis‐ and trans‐1,2‐di‐tert‐butylcyclohexane (cis‐ and trans‐1) and of some of their homomorphs are discussed with respect to the conformations of these compounds. For the cis compounds a chair conformation, in which the rotation of at least one of the substituents is hindered, explains the experimental data (PMR, CMR and IR).IR spectra indicate that in solution the trans compounds exist to a large extent in a non‐chair conformation. Analysis of a Eu(dpm)3 shifted PMR spectrum of trans‐1,2‐bis[2‐(methoxycarbonyl)‐2‐propyl]‐cyclohexane (trans‐2) and of CMR data for trans‐1 shows that certainly a chair conformation with equatorial substituents is not favoured. As it has been shown that trans‐2 has a chair conformation with axial substituents in the crystal, it is concluded that in solution the trans compounds examined probably exist as a conformational mixture, a twist conformation and a chair conformation with axial substituents being the major components.A rationale for these conclusions is offered on the basis of the several severe interactions present in the various conformations.
Synthesis of 2,1‐benzisoxazoles (analogues of psilocine and muscimol)
Authors: du Crocq H. , Lousberg R. J. J. Ch. , Salemink C. A. 
Published: September 2010

AbstractThe synthesis of several 2,1‐benzisoxazoles with substituents at different positions of the six‐membered ring and with a variable aliphatic side‐chain at C‐3 is reported. Anomalous reactions and complications, encountered in this synthesis, are dealt with.
The reactions of 6‐chloro‐ and 6‐bromo‐2,3‐dimethylquinoxaline with potassium amide in liquid ammonia
Authors: Czuba W. , Poradowska H. 
Published: September 2010

AbstractAmination of 6‐halogeno‐2,3‐dimethylquinoxalines resulted in the formation of 5‐amino‐and 6‐amino derivatives. The reaction was found to involve intermediate formation of 5,6‐didehydro‐2,3‐dimethylquinoxaline.
Reactions of 1‐ and 3‐bromoisoquinoline with potassium amide in liquid ammonia. Nucleophilic substitution of 3‐bromoisoquinoline by the ANRORC mechanism
Authors: Sanders Georgine M. , van Dijk M. , den Hertog H. J. 
Published: September 2010

AbstractBoth 1‐ and 3‐bromoisoquinoline are converted by potassium amide in liquid ammonia into the corresponding amino derivatives in excellent yields. It is shown that the amination of 3‐bromoisoquinoline proceeds as for 55% by the SN(ANRORC) mechanism via an open‐chain compound, while the remaining 45% substitution, as well as the substitution in 1‐bromoisoquinoline, occurs probably by the AE mechanism.When heated with ethanolic ammonia at 130°C 3‐bromoisoquinoline is transformed into 3‐aminoisoquinoline to the extent of 27% by the SN(ANRORC) mechanism; thus this mechanism may well occur with other reagents also.
Caractérisation des ions VOCl3Br2− et [VOCl3(CH3CN)]−
Authors: Brunette J. P. , Leroy M. J. F. 
Published: September 2010

Abstract[(C2H5)4N]2VOCl3 Br and (C2H5)4N[VOCl3(CH3CN)] have been synthesized by reaction of VOCl3 with (C2H5)4 NBr and (C2H5)4NI. Conductivity measurements and visible spectra have been obtained from solutions of the compounds in CH3CN. VOCl3Br2− and [VOCl3(CH3CN)]− anions have been characterized in the solid state by infrared spectroscopy: the complex ions are monomeric, with the vanadium most probably five‐coordinated.
On some problems of the hydrogenation of benzene on nickel and nickel‐copper alloys
Authors: van Barneveld W. A. A. , Ponec V. 
Published: September 2010

AbstractA comparison is made of the activity of the Ni catalyst and alloys with 5 and 10 at % Cu, in the hydrogenation of benzene. While at low temperatures (< 100°C) Ni is more active, at higher temperatures the situation is reversed; the reason is the presence of side‐reactions as hydrogenolysis and coke formation. Alloying of Ni with Cu has a much more pronounced effect on the reactions of CC bonds (side reactions) than of CH bonds.
Recherche d'effets stériques dans la réactivité de la norbornanone‐2 par la mesure des effets isotopiques secondaires du deuterium
Authors: Boyer B. , Lamaty G. , Roque J. P. , Geneste P. 
Published: September 2010

AbstractThe following compounds have been prepared: 2‐norbornanone‐3d1 exo, ‐3‐d1 endo, ‐ 3,3‐d2 and 5,6‐d2 endo; the rates of borohydride ion addition and of decomposition of bisulfite addition compounds have been measured in order to explain the high exo side reactivity of norbormyl systems. In both reactions, there is no significant isotope effect due to deuteration at the 5,6 endo positions. This observation can result either from an absence of any steric interaction or from a non‐bonded interaction potential much smaller than usually admitted. The protons in 3‐endo and 3‐exo positions are not equivalent towards the nucleophile approach.
Peroxidation and bromination of thujopsene
Authors: Traas P. C. , van der Linde L. M. , Takken H. J. 
Published: September 2010

AbstractWe have confirmed that treatment of thujopsene (1) with peracetic acid and m‐chloro‐perbenzoic acid occurs exclusively from the side (β) towards the cyclopropane ring in the molecule, while osmium tetroxide reacts from the α‐ as well as from the β‐side. It was found that reaction of the unisolated intermediate epoxide 2 with acetic acid and m‐chlorobenzoic acid yields, besides the thujopsanones (4) and (5), 2β‐hydroxy‐3β‐acetoxythujopsane (7) and 2β‐(m‐chloro‐benzoyloxy)‐3β‐hydroxy thujopsane (3), respectively, and not 2α‐acetoxy‐3β‐hydroxythujopsane (11) and 2α‐(m‐chlorobenzoyloxy)‐3β‐hydroxythujopsane (10) in contrast with what was previously reported by other authors. Reaction of thujopsene with hypobromous acid and bromine yields, in both cases, 3‐bromothujopsene (21).
Ring transformations in reactions of heterocyclic halogeno compounds with nucleophiles (XXXVII). A 15N study on amination and isoxazole formation in reactions of 6‐substituted 4‐chloro‐ and 4‐phenoxypyrimidine 1‐oxides with liquid ammonia and with potassium amide in liquid ammonia
Authors: Peereboom R. , van der Plas H. C. 
Published: September 2010

AbstractTreatment of 4‐chloro‐6‐R‐[1(3)‐15N]pyrimidine 1‐oxide (RCH3, C6H5) with liquid ammonia at − 33°C yields 4‐amino‐6‐R‐pyrimidine 1‐oxide (RCH3, C6H5), which contains no 15N‐label in the amino group. The amino‐dechlorination does not take place according to an SN(ANRORC) mechanism. The same results were obtained with solutions of potassium amide in liquid ammonia at − 75°C. Furthermore, 4‐chloro‐5‐deutero‐6‐phenylpyrimidine 1‐oxide in liquid ammonia yields a 4‐amino‐5‐deutero‐6‐phenylpyrimidine 1‐oxide with the same D content as the starting material, thus excluding an SN(EA) process. It was found that the reaction of 4‐chloro‐6‐methyl‐[1(3)‐15N]pyrimidine 1‐oxide with liquid ammonia at − 33°C and with potassium amide in liquid ammonia at − 75°C, to 5‐amino‐3‐methylisoxazole is accompanied by loss of 15N. The 15N label was unequally distributed over the nitrogen of the ring and the amino group. Two concurrent mechanisms: one, involving the addition of the amide ion to C(2), the other to C(4) of the pyrimidine ring are proposed. Since the 5‐amino‐3‐methylisoxazole obtained from reaction of 6‐methyl‐4‐phenoxy‐[1(3)‐15N]pyrimidine 1‐oxide with potassium amide in liquid ammonia at − 33°C shows no lowering of the 15N content, only an initial addition of the amide ion to C(2) ‐ and not to C(4) takes place in this ring contraction.