Parts-per-Million-Level, Catalytic [3+2]-Annulations for the Asymmetric Synthesis of Methanobenzo[7]annulenes

Abstract

3-Alkyl-lawsones selectively reacted with α-alkyl-nitroethylenes under 500 parts-per-million (ppm) quinine-NH-thiourea-catalysis to furnish the chiral methanobenzo[7]annulenes in up to >99 % ee with >20 : 1 dr and TON up to 1820 through tandem Michael/Henry [3+2]-annulations. These asymmetric ppm-level, catalytic tandem [3+2]-annulations would be highly inspirational for the design of many more ppm-level organocatalytic reactions, and at the same time these final molecules are basic skeletons of antibiotics.

Keywords: annulations; antibiotics; asymmetric catalysis; lawsone; ppm-level catalysis.