B(C 6 F 5 ) 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‐1 H ‐1,5‐benzodiazepines

Abstract B(C 6 F 5 ) 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‐1 H ‐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.