Alkylations of Electron-Deficient Heteroaromatics

Significance

MacMillan and Lee describe an enantioselective conjugate addition of trifluoro(organo)borates to α,β-unsaturated aldehydes 1 catalyzed by amine 2. Potassium styryltrifluoroborate salts 3 and electron-deficient heteroaromatics as their potassium heteroaryl trifluoroborate salts 4 are employed as π-nucleophiles. Tryptophan-derived imidazolidinone catalyst 2 ·HCl converts a broad range of α,β-unsaturated aldehydes into vinyl (5) and heteroaryl (6) addition products, respectively. Good to excellent yields (69-97% yield) and good enantioselectivities (er = 93.5:6.5 up to 98.5:1.5) are obtained. Furthermore, non-traditional regiocontrol as part of a Friedel-Crafts alkylation is achieved (see example two).