Simple and condensed β-lactams. Part 11. Reaction of some p-nitrobenzyl (4-oxoazetidin-1-yl)(triphenylphosphoranediyl)acetates and p-nitrobenzyl (1-oxoisoindolin-2-yl)(triphenylphosphoranediyl)acetate with acetic anhydride–sulphoxide reagents

Abstract

Reaction of the p-nitrobenzyl (4-oxoazetidin-1-yl)(triphenylphosphoranediyl)acetates (1a and b) with the acetic anhydride–DMSO reagent gave mixtures of the acetoxy (2a and b) and methylene derivatives (5a and b), the product ratio depending on the reaction temperature. p-Nitrobenzyl (1-oxoisoindolin-2-yl)(triphenylphosphoranediyl)acetate (6), on similar treatment, furnished the methylene derivative (7) exclusively while, with the acetic anhydride–diphenyl sulphoxide reagent, the acetoxy derivative (8a) was obtained. Type (11) pentacovalent phosphorus derivatives are thought to be the precursors of the acetoxy derivatives (10)[(2) or (8a)]. Although attempts at trapping the type (13) carbenes failed, some observations nevertheless suggest that these carbenes may be intermediates on the pathway leading from the pentacovalent phosphorus (11) to the acetoxy derivatives (10). The methylene derivatives (26)[(5) or (7)], on the other hand, are thought to arise via a Wittig-type reaction of the phosphoranes (27)[(1) or (6)].