B(C₆F₅)₃‐Catalyzed One‐Pot Tandem Diastereoselective Synthesis of cis‐2,3‐Disubstituted 1,2,3,4‐Tetrahydroquinoxalines and cis‐2,4‐Disubstituted 2,3,4,5‐Tetrahydro‐1H‐1,5‐benzodiazepines

Abstract

B(C6F5)3‐catalyzed one‐pot tandem cyclization/hydrosilylation of easily accessible 1,2‐diaminobenzenes and 1,2‐ and 1,3‐diketones with polymethylhydrosiloxane (PMHS) has been developed for step‐economic diastereoselective synthesis of cis‐2,3‐disubstituted 1,2,3,4‐tetrahydroquinoxalines and cis‐2,4‐disubstituted 2,3,4,5‐tetrahydro‐1H‐1,5‐benzodiazepines. This metal‐free catalytic protocol provides access to various differently substituted products in 53–95% yield and with diastereoselectivities ranging from 6:1 to 20:1. The diastereoselectivity strongly depends on the choice of hydrosilane, with PMHS being optimal. The reaction is operationally simple and readily scaled up, and proceeds without exclusion of air and moisture.