Bernard A. J. Clark

Formation of certain substituted 5H-pyrrolo[2,3-b]pyrazines by thermal cyclisation of pyrazinylhydrazones and a route to 5H-pyrazino[2,3-b]indole; a synthesis of 5H-pyrrolo[2,3-b] pyrazine and some of its properties

Thermal (non-catalytic) cyclisation of the pyrazinylhydrazones (6a—i) caused ring closure on to the carbon atom of the pyrazine nucleus to give the 3-substituted and 2,3-disubstituted 5H-pyrrolo[2,3-b]pyrazines (7a—g), (8), and (9), respectively. 6,7,8,9-Tetrahydro-5H-pyrazino[2,3-b]indole (7g) was dehydrogenated to the parent pyrazino[2,3-b]indole (15). Pyrrolo[2,3-b]pyrazine (7h) has been obtained from 2-amino-3-methylpyrazine and some of its properties have been investigated.

Diazaindenes (azaindoles). Part VI. Preparation and some properties of 1,7-diazaindene 7-oxide and 6,7,8,9-tetrahydro-γ-carboline 2-oxide

Treatment of the N-acetyl derivatives of 1,7-diazaindene and 6,7,8,9-tetrahydro-γ-carboline with m-chloroperoxybenzoic acid gave the 7-oxide (6) and the 2-oxide (13), respectively. The reaction of the N-oxide (13) with acetic anhydride yielded 6,7,8,9-tetrahydro-γ-carbolin-1(2H)-one (24), and the 7-oxide (6) gave 1,7-diazainden-6(7H)-one (26). 1-Chloro-6,7,8,9-tetrahydro-γ-carboline (14) was obtained directly from the N-oxide (13), but the 7-oxide (6) gave 4-chloro-1,7-diazaindene (8); the chlorine atom in (8) was not easily replaced by nucleophiles. The tetrahydro-γ-carboline N-oxide (13) was converted into 1-cyano-(16) and 1-anilino-tetrahydro-γ-carboline (18).

Diazaindenes (azaindoles.) Part V. Synthesis, spectra, and tautomerism of 1,5-diazainden-4(5H)-one, 1,4- and 1,6-diazainden-2(3H)-one, and some 3-substituted derivatives

1,5-Diazaindene 5-oxide has been prepared and rearranged, giving 1-acetyl-1,5-diazainden-4(5H)-one (1). Compound (1) has also been obtained from either (a)cis-3-(pyrrol-2-yl)acrylic acid or (b) 1,5-oxazainden-4(5H)-one. 1,4- and 1,6-Diazainden-2(3H)-one and some 3-substituted derivatives have been synthesised from the corresponding chloronitropyridines. Spectra show that the location of the nitrogen atom in the pyridine ring and the type of 3-substituent markedly influence the position of tautomeric equilibrium.

Preparation and some reactions of 2,2-diaryl-2H-imidazole 1-oxides

The acid-catalysed condensation of diphenylmethyleneamines with various α-hydroxyimino-ketones (1a–f) gave 2,2-diphenyl-2H-imidazole 1-oxides [(2a–f), and (8)]. These compounds react as nitrones with lithium aluminium hydride, methylmagnesium iodide, and dimethyl acetylenedicarboxylate. However, the reaction of 4-methyl-2,2-diphenyl- and 2,2,4-triphenyl-2H-imidazole 1 -oxides with sodium borohydride gave the corresponding 2H-imidazoles. Curtis rearrangement of 5-methyl-2,2-diphenyl-2H-imidazole-4-carbonyl azide 3-oxide (6) gave 7-methyl-5,5-diphenylimidazo[1,5-b][1,2,4]oxadiazol-2(5H)-one (14).

Gas-phase pyrolysis of 1-(2-azidophenyl)imidazole

Flash vacuum pyrolysis (FVP) of the azide 4 leads to imidazo[1,2-a]benzimidazole 8 exclusively, via highly regioselective insertion of the triplet nitrene intermediate 5 into the 2-CH bond of the imidazole ring. The X-ray crystal structure and NMR spectroscopic properties of 8 are discussed in detail.

Novel gas-phase cyclisation reactions of 2-(1-pyrazolyl)phenylnitrenes

Flash vaccuum pyrolysis of the azide 3 gives a mixture of pyrazolobenzotriazole 2, quinoxaline 5 and pyrazolobenzimidazole 4 derived from the corresponding nitrene.