Formation of isocyanates by deoxygenation of C-nitrosocarbonyl compounds

Abstract

The cycloadduct (1a) of 9,10-dimethylanthracene (2)(hereinafter referred to as DMA) and nitrosocarbonylbenzene decomposed in benzene at 80 °C in the presence of triphenylphosphine to give DMA, triphenylphosphine oxide, and phenyl isocyanate in high yield. The corresponding adducts of 4-chloro-(1b), 4-methoxy-(1c), and 4-nitro-nitrosocarbonylbenzene (1d) behaved likewise. The cycloadduct of DMA and 4-methoxybenzylnitrosocarbonylmethane (1e) and of DMA and 1-(4-methoxyphenyl)-2-nitrosocarbonylethane (1f) gave lower (20–30%) yields of isocyanates. The rates of decomposition of the adduct (1a) in the presence of either the conjugated diene thebaine (3) or various phosphorus(III) derivatives were the same within experimental error. A similar observation was made for compound (1d). The formation of isocyanates is believed to involve slow dissociation of the cycloadducts followed by rapid deoxygenation of the transient nitrosocarbonyl compounds by triphenylphosphine. Stable complexes (8) of triphenylphosphine oxide with N-(4-nitrophenyl)-N′-propylurea and N-(4-nitrophenyl)-N′-phenylurea are described.