O-Quinone monoimine

The photochemical addition of both aliphatic and aromatic aldehydes to o-quinones monoimines has been widely used in the preparation of oxazoles [Eq. (92)].340 An intermediate amide has been isolated in a number of cases, and can be thermally converted into the oxazole. The reaction, therefore, does not appear to be a cycloaddition. An analogous addition occurs between o-quinones and aldehydes, and the photoproducts have been shown to have an acyclic structure341 rather than the previously assigned 1,3-dioxole structure. 

As part of an examination of an oxidative coupling of methyl 6-hydroxyindole-2-carboxylate with primary amines which enabled the development of a facile preparation of 2-substituted methyl pyrrolo[2,3-e]benzoxazole-5-carboxylates, the reaction of this indole with 1,2-diaminoethane and excess Mn02 gave compound (83) in an apparent intramolecular interception of a transient intermediate o-quinone monoimine (Equation (46)) <88JOC5163>. 

Thiophenes can act as dienophiles in Diels-Alder reactions with electron-poor dienes such as hexachlorocyclopen-tadiene, tetrazines, or o-quinone monoimines. The masked o-benzoquinone 64 can undergo inverse electron demand cycloadditions with thiophene itself or simple derivatives such as 2-methyl-, 2-methoxy-, and 2,4-dimethylthiophene (Scheme 5) <2001TL7851>. Depending on the substitution pattern on the thiophene skeleton, different cycloadducts can be observed. The basic thiophene skeleton gives rise to a bis-adduct 65. By blocking the second double bond with a methyl or methoxy group, a 1 1 adduct 66 or 67, respectively, is obtainable in moderate yield. 

Hetero-l-oxabutadiene systems that have been shown to participate as 47t components of Diels-Alder reactions include vinylnitroso compounds (31, 2-aza-l-oxabutadiene, Chapter 9, Section 3), fV-acylimines (32) as well as aromatic and aliphatic acylisocyanates (33, X = O) and isothiocyanates (33, X = S, 3-aza-l-oxabutadiene, Chapter 9, Section 3), acylnitroso compounds (34,2-aza-l, 4-dioxabutadiene, Chapter 9, Section 3), selected 4-aza-l-oxabutadienes, e.g., 35, including o-quinone monoimines (36,... 

N. Bodipati, R.K. Peddinti, Chemical generation of o-quinone monoimines for the rapid construction of 1,4-benzoxazine derivatives, Org. Biomol. Chem. 10 (2012) 1958-1961. 

Reactions of enamines with monoimines of o-quinones afford polycylic compounds 228 with an oxazine ring (86MI2).Trifluoroacetylation of enamines with trifluoroacetic acid takes place in the /3-position of the enamine. Ketones (229) thus formed in an acidic medium afford fused 1,3-oxazines (230) (82JOC3339). Treatment of amines with silyl isothiocyanate gives not only pyrimidine derivatives but also l,3-oxazine-4-thiones (231) (81CCC2696). 

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