Synthesis of Dithieno[2,3-b:4′,3′-d]siloles and Their Selective Bromination

The efficient synthesis of novel unsymmetrical dithienosiloles, 7,7-dimethyl-4,6-di­(trimethylsilyl)-dithieno­[2,3-b:4′,3′-d]­silole (1) and 7,7-dimethyl-2,4,6-tri­(trimethylsilyl)-dithieno­[2,3-b:4′,3′-d]­silole (2) has been developed by intramolecular silole formation with 4,4′-dibromo-2,2′,5,5′-tetrakis­(trimethylsilyl)-[3,3′]­bithienyl (3) as the starting material in the presence of t-BuLi. Upon treatment with N-bromosuccinimide (NBS) under controlled conditions, dithieno­[2,3-b:4′,3′-d]­silole was selectively brominated to produce mono-, di-, and tribrominated dithieno­[2,3-b:4′,3′-d]­siloles in good yields. The crystal structures of the title compounds are described.