Organocatalytic Vinyl and Friedel−Crafts Alkylations with Trifluoroborate Salts

This is the first use of vinyl and heteroaryl trifluoroborate salts as viable substrates for amine-catalyzed conjugate additions and can enable nontraditional regiocontrol as part of a Friedel−Crafts pathway.

Abstract

Herein we report the first use of vinyl and heteroaryl trifluoroborate salts as viable substrates for amine-catalyzed conjugate additions. The application of LUMO-lowering iminium catalysis has enabled the highly regio- and enantioselective 1,4-addition of rationally designed trifluoroborate salt nucleophiles to α,β - unsaturated aldehydes. Imidazolidinone 2 •HCl was found to catalyze the addition of various BF 3 K-derived heteroaryl and vinyl species to a range of enals with excellent levels of enantioselectivity. Importantly, the use of these salts can enable nontraditional regiocontrol as part of a Friedel−Crafts pathway. Boronic acids can also be employed as viable π-nucleophiles for these asymmetric conjugate additions provided that in situ activation to the corresponding boronate species is accomplished. While BF 3 K salts are routinely employed in transition metal catalysis, to our knowledge, this is the first use of this activation group for organic catalysis or Friedel−Crafts alkylations.