Homo- and Heteroannulation of sp3 C-H Bonds in Acetophenones for Divergent Synthesis of Thienothiazoles.

A synthesis of fused thieno[3,2-d]thiazoles via direct functionalization of C(sp3)–H bonds in acetophenones was reported. The transformation is divergent to afford either 2-phenylbenzo[4,5]thieno[3,2-d]thiazoles or benzo[4,5]thieno[3,2-d]thiazol-2-yl(phenyl)methanones. Cross-coupling of acetophenones with C–H bonds in phenylacetic acids, methylazaarenes, and aldehydes was also feasible. Excellent tolerance of functionalities was observed. Our method marks a rare functionalization of C(sp3)–H bonds in acetophenones to obtain heterocycles in the absence of prefunctionalized oxime esters.