Reaction of chlorosulfonyl isocyanate with nitrones: an efficient method for the synthesis of cyclic enamides and 2h-pyrroles

Abstract

Reaction of chlorosulfonyl isocyanate (CSI) with nitrones (derived from cyclic conjugated ketones), 1 - 7 and 3,4-dihydro-2H-pyrrole-1-oxides, 15a - f ,-has been studied. Nitrones, 1 - 7 , react with CSI to form the enamidea, 8 , 10 - 14 , and the cyclil-amide, 9 , in yields ranging from 33 to 72 %. However, the 5,4-dihydro-2H-pyrrole-1-oxides, 15a - e , on reaction with CSI gave the 2H-pyrr-oles, 16a - e , in good yields. The 3,4-dihydro-2H-pyrrole-1-oxide, 15f , under similar experimental conditions gave the pyrrolidone, 17f , in 40% yield. Plausible mechanisms for the above mentioned rearrangement and conversions have been proposed with experimental evidences.