Hydrogen-Bonding Assisted Catalytic 1,2-Addition Reaction of Trifluoropyruvate with 2,4-Dihydrocylopenta[b]indoles

Abstract

CF₃-substituted tertiary alcohols are valuable as biologically active compounds, but the synthesis of the corresponding cyclopentadiene derivatives remains challenging. The DABCO-catalyzed 1,2-addition reaction of trifluoropyruvates with 2,4-dihydrocyclopenta[b]indoles has been developed, affording CF₃-substituted tertiary alcohols in up to 90% yield and with up to >99:1 dr. The catalytic reaction is facilitated by hydrogen bonding (N–H···N) between the cyclic tertiary amine and the indole moiety. Additionally, Et₃N (1.0 equiv) can promote the retro-1,2-addition reaction of the CF₃-subsituted tertiary alcohols, yielding dihydrocyclopenta[b]indole 1 in up to 72% yield.