Chiral Brønsted acid catalyzed Friedel-Crafts alkylation reactions

Enantioselective conjugate addition of alkenylboronic acids to indole-appended enones

An enantioselective addition of alkenylboronic acids and alkynylboronic esters to unprotected indole-appended enones is reported. This transformation proceeds with high enantioselectivity and high product yields via the use of catalytic amounts of 3,3'-bis(pentafluorophenyl)-BINOL and Mg(Ot-Bu)(2). A range of α-branched indole derivatives are available from the transformation.

Direct synthesis of chiral 1,2,3,4-tetrahydropyrrolo[1,2-a]pyrazines via a catalytic asymmetric intramolecular aza-Friedel-Crafts reaction

The direct asymmetric intramolecular aza-Friedel-Crafts reaction of N-aminoethylpyrroles with aldehydes catalyzed by a chiral phosphoric acid represents the first efficient method for the preparation of medicinally interesting chiral 1,2,3,4-tetrahydropyrrolo[1,2-a]pyrazines with high yields and high enantioselectivities. This strategy has been shown to be quite general toward various aldehydes and pyrrole derivatives.

N-heterocyclic carbene and Brønsted acid cooperative catalysis: asymmetric synthesis of trans-γ-lactams

An efficient enantioselective approach to form trans-γ-lactams in up to 99% yield, 93% ee, and >20/1 dr using unactivated imines has been developed. The cyclohexyl-substituted azolium and the weak base sodium o-chlorobenzoate are most suitable for this transformation. Notably, the process involves cooperative catalysis by an N-heterocyclic carbene and a Brønsted acid.

Regioselective alkylation of heteroaromatic compounds with 3-methyl-2-quinonyl boronic acids

Reactions of heteroaromatic compounds with 3-methyl substituted 2-quinonyl boronic acids proceeded by 1,4-addition followed by spontaneous protodeboronation, leading directly to the Friedel-Crafts alkylation products instead of the commonly observed alkenylation derivatives resulting from quinones. The boronic acid acts as a temporary regiocontroller, making the system a highly reactive quinone equivalent and opening a direct access to 5,5-disubstituted cyclohexene-1,4-diones.