Transformations of penicillin. Part III. A new route to 2,2-dimethyl-6β-phenylacetamidopenam-3α-ol S-oxide and its esters; o-nitrobenzoate as a protecting group for alcohols and phenols

Abstract

Esters of the title compound have been obtained by rearrangement of aroyl penicillanoyl peroxides, followed by decarboxylation. Certain of the aroyl esters so produced have been epimerised at position 6 with selected secondary amines. Conditions for the liberation of the title alcohol from some of its aroyl esters have been established. Thus, the 2,4-dinitrobenzoate can either be photohydrolysed, by irradiation in aqueous tetrahydrofuran, or reduced with sodium borohydride. o-Nitrobenzoate is a potentially useful protecting group for alcohols and phenols since the group can be removed in high yield by reduction with zinc dust and ammonium chloride; the alcohol is liberated with formation of 2,1-benzisoxazolin-3-one. In this manner the title alcohol was obtained from its o-nitrobenzoate in 95% yield.