CYCLOADDITION OF C,N-DIARYLNITRONES TO 2-BUTENOLIDE - SYNTHESIS OF 2,3,6,6A-TETRAHYDROFURO[3,4-D]ISOXAZOL-4(3AH)-ONE

The cycloadditions of four C,N-diaryl nitrones (1-4) to the 5-membered conjugated lactone 2-butenolide were investigated. Two stereoisomeric 2-phenyl-3-aryl-2,3,6,6a-tetrahydrofuro[3,4-d]-isoxazol-4(3aH)-one cycloadducts and a ring-opened butanolide derivative were obtained in each case. The structure and stereochemistry of the products were determined by detailed NMR studies. The regiochemical course of the cycloadditions is explained, and the genesis of the ring-opened product rationalised.