Exocyclic sulfonamides

The reaction of o-halobenzenesulfonamide 256 with allene 257, in the presence of Pd(0), affords the exocyclic alkene 258 via nitrogen attack on the 7t-allyl Pd-intermediate 259 (Scheme 35) <2001EJ0707>. The related cyclopropane product 260, formed in high yields in the analogous reactions of carboxamides, is not observed for the sulfonamide substrate 256. 

Harmata et al. have developed a tandem Sonogashira/nitrogen-addition reaction of acetylenes 261 to sulfonamide 262 to prepare S(vi)-oxidized compounds 263 and 264 (Scheme 36) <20050L143>. When R = alkyl (e.g., Pr"), the 1,2-thiazine 263 is the major product (70%) formed via a endocyclization process, along with a minor amount (20%) of exocyclized product 264, while the five-membered ring product 264 (81%) is preferred when R= Ph. 

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