Ligand free Pd catalyzed cyclization-influence of steric hindrance

Abstract

Synthesis of sultams was performed using ligand free palladium catalyst following Heck cyclization. The diverse synthesized intermediates in this strategy includes halogenated sulfonyl chloride, alkyl/aryl sulfonamides, N-alkylation using halogenated alkenyl reagents followed by improved Heck cyclization with Pd(OAc)2/DIPA in 1-methyl-pyrolidin-2-one/toluene. In this way, isomeric six membered sultams with endocyclic & exocyclic double bonds (benzothiazine) and seven membered (thiazipene) were obtained. Endocyclic double bond isomer was dominates in respect of yield over the exocyclic double bond isomer. The isolated amounts of endocyclic sultams and thiazipene were almost equal in amounts. The intermediates and final products were characterized using IR, 1H-NMR, 13C-NMR and EI-MS techniques.