Cycloadducts of C-nitrosocarbonyl compounds and ergosteryl acetate; [3,3]sigmatropic rearrangements of N-aroyl-3,6-dihydro-1,2-oxazines

Abstract

Oxidation of acetohydroxamic acid with tetraethylammonium periodate in the presence of ergosteryl acetate (3) gave a single cycloadduct (4a) arising from 1,4-addition of the nitroso group of nitrosocarbonylmethane to the diene system of (3). In contrast, nitrosocarbonylbenzene, generated by oxidation of benzohydroxamic acid or by thermal dissociation of the 9,10-dimethylanthracene adduct (12; R = Ph), gave two 1,4-adducts, (4b) and (5b), with (3). The adduct (5b) isomerised at 60 °C to give a dioxazine (6b), formally an adduct of nitrosocarbonylbenzene, acting as a 4π-electron component, with the 5,6-double bond of (3). However, the isomerisation still took place in the presence of triphenylphosphine, an efficient trap for C-nitroso-compounds, and must therefore have occurred by an intramolecular, [3,3]sigmatropic rearrangement. 4-Bromo-, 4-methoxy-, and 4-nitro-nitrosocarbonylbenzene reacted similarly with (3) whereas 2,4,6-trimethylnitrosocarbonylbenzene gave (4f) as the sole adduct. Adducts of pyrocalciferyl acetate (21) and isopyrocalciferyl acetate (22) with nitrosocarbonylbenzene and of ergosteryl acetate with the nitrosoimine (26) have also been prepared.