Benzimidazolinones rearrangements

Despite the typical use of the 1,5-dienic system in the hetero-Cope rearrangement the participation of triple bonds, C=N and C=C, in the [3,3]-sigmatropic rearrangement was also reported. Synthesis of A-substituted benzimidazolinones 175 by a hetero-Cope rearrangement of the adduct 174 formed by reaction of A-arylhydroxamic acids 172 with cyanogen bromide 173 in the presence of triethylamine and at low temperatures was reported by Almeida, Lobo and Prabhakar (equation 51). 

Saczewski and Debowski reported the l,4-diaza-3-oxa-Cope rearrangement of N-cyanate anilides (equation 52). Prototropic rearomatization of 176 and internal nucleophilic addition afford the corresponding benzimidazolinone 177, usually in moderate yields (32-78%). A concerted [3,3]-sigmatropic rearrangement is proposed based on the absence of para rearrangement product that usually results from homolysis or heterolysis of the N—O bond followed by recombination of the two radicals or ions. 

Secondary ketoenamines react with electrophilic diazenes to give products which undergo rearrangement to an adduct which affords benzimidazolinones after subsequent cyclization322. In the case of tertiary a-enaminones, l,3,4-oxadiazole-2-ones, as unstable intermediates of a [4 + 2]-cycloaddition, can be obtained323 (equation 241). 

Allyl ethers situated on the imidazole moiety in this system show interesting behavior. 2-Allyloxybenzimidazole affords a quantitative yield of l-allyl-2-(3.flr)-benzimidazolinone on heating at 180° [Eq. 7]22b. On the other hand, 1-allyloxybenzimidazole (12) does not rearrange on heating even at its decomposition point. This observation is in line with the findings in the pyridine series where 2-allyloxypyridine-l-oxide rearranges irreversibly to the l-allyloxy-2-pyridone. 

In what appears to be a related reaction, benzimidazole Af-oxides give rise to ben-zimidazolinones as by-products when treated with an acyl halide in the presence of alkali. With tosyl chloride the sole product is the benzimidazolinone (111) which may be formed as in Scheme 50. The N rearrangement could also take place via the oxaziridine (112) <73JCS(P 1)705). 

Hydrogen transfer from hydrazobenzene to benzofuroxan (622) results in azobenzene and o-benzoquinone dioxime (623). Compound (622) reacts with formaldehyde to yield the benzimidazolinone (624). Chlorobenzofuroxan aldehyde condenses with derivatives of hydroxylamine or hydrazine to yield oximes or hydrazones (625 R = OH, OMe, NHPh, NMe2, etc.), which rearrange thermally to indazoles (626). Treatment of 7-methoxy-4-nitro-benzofurazan 1-oxide with aqueous potassium hydroxide affords a mixture of the corresponding 7-hydroxy-compound (627) and the rearranged 5-hydroxy-4-nitrobenzofuroxan (628). ... 

---