Organophosphorus intermediates. VIII. The synthesis of some 2,6-dioxo-1,2,3,4,6,7,8,8a-octahydro-2λ⁵-isophosphinoline derivatives

Abstract

Methyl 1-methoxy-1,4-dioxo-1λ⁵-phosphorinan-3-carboxylate (3) adds readily to but-3-en-2-one to give an adduct (5) which cyclizes under mild non-aqueous conditions to the novel tricyclic compound(6). Substance (5) may be cyclized to mixtures of bicyclic derivatives with either acid or base but the combination LiL/LiOH affords 2-hydroxy-1,2,3,4,8,8a-hexahydroisophosphinolin-6(7H)-one 2-oxide (7a) in an overall yield of 65%. ¹H, ¹³C and ³¹P n.m.r., and mass spectra are reported and discussed.