Umpolung Reactivity of Ynamides: An Unconventional [1,3]-Sulfonyl and [1,5]-Sulfinyl Migration Cascade.

A regioselective sulfonyl/sulfinyl migration cycloisomerization cascade of alkyne-tethered ynamides is developed in the presence of XPhosgold catalyst. This reaction is the first example of a general [1,3]-sulfonyl migration from the nitrogen center to the β-carbon atom of ynamides, followed by umpolung 5-endo-dig cyclization of the ynamide α-carbon atom to the gold-activated alkyne, and final deaurative [1,5]-sulfinylation. This process allows the synthesis of peripherally decorated unconventional 4-sulfinylated pyrroles with broad scope from N-propargyl-tethered ynamides. In contrast, N-homopropargyl-tethered ynamides undergo intramolecular tetradehydro Diels-Alder reaction to provide 2,3-dihydro-benzo[f]indole derivatives. Control experiments and density-functional theory studies were used to study the reaction pathways.