REDUCTIONS, REDUCTIVE ALKYLATIONS, AND INTRAMOLECULAR CYCLIZATIONS OFACYL SILANES WITH SAMARIUM DIIODIDE OR TRIBUTYLTIN HYDRIDE

A series of acyl silanes including aliphatic-, aromatic-, and bis-acyl silanes, as well as the acyl silanes bearing other substituents such as a bromine atom and alkenyl, succinimide, and carbonyl groups, were prepared, and their reactions with samarium diiodide or tributylstanna ne were studied. The reactions of acyl silanes occurred in various man ners such as reductions, reductive alkylations, intramolecular radical cyclizations, pinacol couplings, aldol reactions, and Tishchenko reac tions, depending on the nature of substrates and reaction conditions. Acyl silanes were generally reduced to give the corresponding a-silyl alcohols without transfer of silyl groups. Intramolecular radical cycl izations of 5-hexenoyl silanes and 1-silyl-1,5-pentanedione were reali zed to give cl-silyl cyclopentanols and 1,2-cyclopentanediol derivativ es, respectively. On treatment with samarium diiodide in tetrahydrofur an, 1-(trimethylsilyl)-1,6-hexanedione underwent a pinacol coupling re action in the presence of t-BuOH, whereas it underwent a Tishchenko re action in the presence of MeOH. The Tishchenko reaction of 1-silyl-1,5 -pentanedione gave a delta-silyl-delta-lactone. On treating with samar ium diiodide, 1-(trimethylsilyl)-1,5-hexanedione and 1,5-bis(trimethyl silyl)-1,6-hexanedione, underwent, respectively, intramolecular aldol reactions.