Joseph H. Boyer

Thermal and photochemical α-carbon–carbon cleavages in imines

Autoxidation produced cyclohexyl isocyanide and benzoic acid from N-cyclohexyl-1,3-diphenylpropan-2-imine (16b), and 6-cyclohexyaminodibenzo[a,c]cyclohepten-5-one (24) from N-cyclohexyl-5,7-dihydrodibenzo[a,c]cyclohepten-6-imine (17b). The α,α-cleavage required for the formation of the isocyanide was attributed to a ready fragmentation of the intermediate 4-cyclohexylimino-3,5-diphenyl-1,2-dioxolan-3-ol (22).Photolysis of 3,4-dihydro-3-imino-1,9-di-t-butyl-1,4-ethenonaphthalen-2(1H)-ones (14) and of 3-imino-2,2,4,4-tetramethylcyclobutanones (15) resulted in extrusion of isocyanides and carbon monoxide. Other products included 1,3-di-t-butylnaphthalene from (14), tetramethylethylene from (15), an adduct (38) of tetra-methylcyclopropanone and furan (solvent) from (15b and c) and 2-isopropylidene-4,4-dimethyl-3-phenyliminooxetan (39) from (15c). Irradiation at 254 nm transformed the imine (16b) into 1,2-diphenylethane and N-cyclohexyl-2-phenylvinylideneamine (43) but had no effect on the N-cyclohexylthujan-3-imine (18) in cyclohexane or isopropyl alcohol. The N-unsubstituted five- and seven-membered ring α-cyanocycloalkanimines were inert to irradiation at 254 nm.Reactions in the mass spectrometer correlated with thermal and photolytic extrusion of the C2O2 bridge from 1,4-dihydro-1,9-di-t-butyl-1,4-ethenonaphthalene-2,3-dione (9), with photolytic extrusion of the RNC2O bridge from the corresponding monoimines (14), and with the photolysis of the imine (16b) to give the vinylideneamine (43). An intense M+– CO peak was also obtained for the diketone (9). Isocyanides were detected as RNC+ from the imines (14a—e), (15b), (17b), and (18b).

Fragmentation-rearrangement of Δ3-oxadiazolin-5- and 3-ones

2-Phenylbenzimidazole (6)(major product) and 2-phenylbenzoxazole (10) were obtained from 2,3-diphenyl-Δ3-1,2,4-oxadiazolin-5-one (2) by thermolysis (250 °C, diphenyl ether), and by photolysis (254 nm, dioxan). Photolysis also isomerised the oxadiazolinone (2) into 2,5-diphenyl-Δ4-1,2,4-oxadiazolin-3-one (8), and 2,4-diphenyl-Δ2-1,3,4-oxadiazolin-5-one (9). Similar thermolysis and photolysis of 2-benzyl-3-phenyl-Δ3-1,2,4-oxadiazolin-5-one (3) gave cyaphenine (11) and lophine (12). The diphenylazomethine nitrene (14) can be the precursor to the imidazole (6) and the transformations (2)→(10) and (3)→(11)+(12) can proceed from the appropriate carbamic acid derivative [(16) or (23)], which are available from (2) or (3) by a 1,3-migration of oxygen from nitrogen to carbon.

Fragmentation of 2-(2-azidophenyl)pyridine and isomerisation of 5λ5σ3-pyrido[1,2-b]indazole

The action of heat on 2-(2-azidophenyl)pyridine (1) quantitatively produced 5λ5σ3-pyrido[1,2-b]indazole (7) in tetralin, mesitylene, or acetophenone, and gave a nearly 1 : 1 mixture of (7) and 2-(2-aminophenyl)pyridine (3) in di-n-butylamine. The photoreaction of the azide (1) in cyclohexane was complete after 3 h, and gave quantitatively a 1 : 2 mixture of pyrido[3,2-b]indole (4) and the pyridoindazole (7) from irradiation at 254 or 300 nm and a 1 : 5 mixture from irradiation at 350 nm. Irradiation of a mixture of the azide and acetophenone (1 : 85) in cyclohexane gave the amine (3)(39%) and lesser amounts of the heterocycles (4) and (7), and irradiation in diethyl or di-n-butylamine transformed the azide into the corresponding 2-dialkylamino-3-(2-pyridyl)-3H-azepine (5)(51 and 65%). 5λ5σ3-Pyrido[1,2-b]indazole (7) in tetrahydrofuran was converted (40%) into the pyridoindole (4)(100%) by irradiation at 254 nm for 136 h. Solvent and sensitisation effects on the photolysis of the azide (1) and the indazole (7) are presented. Mechanisms for the thermal and photochemical reactions are discussed.

A unique formation of an isoxazoline-N-oxide from nitrodibromoacetonitrile and tetramethylethylene

La reaction a lieu dans le dichloromethane; le dibromo-2,3 dimethyl-2,3 butane est egalement obtenu

Mesoionic oxadiazolium-olates and oxatriazolium-olates from aryl isocyanides and nitroform

Nitroform converted p-nitrophenyl isocyanide into the mesoionic 3-p-nitrophenyl-1,2,3-oxadiazolium-5-olate (2) and 3-p-nitrophenyl-1,2,3,4-oxatriazolium-5-olate (3), together with p-nitroaniline; it converted p-tolyl isocyanide into the mesoionic 3-(2-nitro-4-methylphenyl)-1,2,3-oxatriazolium-5-olate together with 2-nitro-4-methylaniline and p-methylaniline.

Nitrosamines from tertiary amines and dinitrogen tetraoxide

A preparative nitrosolysis of aliphatic acyclic and cyclic tertiary monoamines to nitrosamines was brought about by treatment with dinitrogen tetraoxide in carbon tetrachloride at 0–45 °C. Dealkylation was restricted, where applicable, to demethylation. Competitive oxidation to an amide was observed in the formation of dibutylformamide from tributylamine. Diamine dinitrate salts, without nitrosamine formation, were obtained from 1,4-dimethylpiperazine and 1,4-diaza[2.2.2]bicyclo-octane; however, each dinitrate salt thermolysed at 180–200 °C to give a small amount of 1,4-dinitrosopiperazine. In acetic anhydride dinitrogen tetraoxide converted amines less efficiently, gave lower yields of nitrosamines, was less selective in dealkylation, and introduced the formation of by-products.

Oxidation of nitrobenzofuroxans

Monoperoxosulphuric acid oxidized 4-nitro-benzofuroxan into 1,2,3-trinitrobenzene (80%) and 4, 6-dinitrobenzofuroxan into 1,2,3,5-tetranitrobenzene (100%).

Thermolysis of diphenyl-Δ3- and diphenyl-Δ4-1,2,4-oxadiazolinones

Thermolysis gave 2-phenylbenzoxazole from 2,3-diphenyl-Δ3-1,2,4-oxadiazolin-5-one and from 2,5-diphenyl-Δ4-1,2,4-oxadiazoline-3-one and also gave benzoxazolinone from the latter by new ring transformations which accompanied the formation of 2-phenylbenzimidazole and 2,4-diphenyl-Δ2-1,3,4-oxadiazolin-5-one as respective major products.

Formimidoyl cyanide and isocyanide from azidoacetonitrile by photolysis

Photoelimination of nitrogen from azidoacetonitrile (1) produced formimidoyl cyanide (2). At –196 °C further irradiation transformed the cyanide (2) into formimidoyl isocyanide (3); both (2) and (3), detected by i.r. absorption, can be intermediates in the formation of hydrogen cyanide and adenine (4) from a solution of (1) irradiated at 25–40 °C. Photodissociation of N-ethyl-(5a), N-isopropyl-(5b), and N-t-butyl-formimidoyl cyanide (5c) gave the corresponding N-alkyl isocyanide (7a–c)(3 %) at 25–40 °C and in detectable amounts at –196 °C. Azidoacetonitrile (1) at 125 °C dimerised to give 5H,10H-ditetrazolo[1,5-a:1′,5′-d]pyrazine(15).

Nitrosamines from N,N-disubstituted hydrazines

Photolysis of nitro hydrazones (from N,N-disubstituted hydrazines and tetranitromethane) gave nitrosamines.