Alkali-amide-catalyzed divergent sp2 and sp3 C–H bonds alkylation of alkylthiophenes with alkenes

Abstract

The divergent transformations of different C–H bonds in a given substrate represent the state of the art in C–H functionalization reactions, wherein there is a need for precise control of the selectivity of the catalyst. Simply by using alkali amide catalysts, we herein selectively achieved the addition of divergent sp² and sp³ C–H bonds of alkylthiophenes to alkenes. Lithium diisopropylamide (LDA) underwent the deprotonation of the C5 sp² C–H bond and addition to alkenes to afford C5 alkylation products. Potassium bis(trimethylsilyl) amide (KHMDS) failed to undergo the deprotonation but established a deprotonative equilibrium between the C5 sp² C–H bond and the benzylic sp³ C–H bonds. Further alkylation with alkenes, however, selectively took place at the benzylic sp³ C–H bond. This work presents the divergent alkylation products of alkylthiophenes, and demonstrates the interesting and distinct behaviors of potassium and lithium amides.