The Rh and Ir catalyzed silylcarbocyclization (SiCAC) reaction and cascade silylcarbocyclization reactions

Transition-metal-catalyzed reactions have become an increasingly important tool in the synthesis of complex molecules. The exploration and optimization of the type I Silylcarbocyclization (SiCAC) and related reactions are discussed in this work. The rhodium-catalyzed SiCAC reaction, using 1% Rh(I) catalysts and 1 equivalent of HSiMe2Ph under 1 atm of CO, of 1,6-enynes produced a combination of five membered ring products containing an exo-silylmethylene group with either a methyl or formylmethyl group at the 2 position. These two products are referred to as the SiCAC or CO-SiCAC products, respectively. The SiCAC reaction was shown to be capable of accepting the presence of a range of other functional groups including amines, esters, ethers and other more remote olefins. Experiments with 1,5-alkynals showed that the type I SiCAC reaction can also be used to produce 2-exo-silylmethylene-cyclopentanols in excellent yield.;The effects of varying temperature, concentration, CO-pressure, solvent, and the catalyst used, on the SiCAC reaction were investigated. Using the correct combination of these factors, either the SiCAC or CO-SiCAC product can be produced with good selectivity and in good to excellent yield.;The Rh-catalyzed SiCAC reaction was also conducted on both ( E)- and (Z)-dodec-6-ene-1,11-diynes to produce the (R*,R*)-bis(exomethylenecylopentyl) and (R*,S*)-bis(exomethyenecylopentyl) diastereoselectively, in moderate yield. This demonstrates that this reaction is capable of undergoing cascade cyclizations to produce complex polycylic structures. Cascade cyclization reactions were also conducted on 1,6,11-triynes to produce a mixture of silylated and non-silyated aromatic products resulting from three consecutive cyclizations followed by either beta-hydride or beta-silyl elimination. In addition to this, a bis[silylmethylcyclopentene] resulting from two cyclizations followed by 1,6-hydrosilylation was produced. Possible mechanisms for the formation of these products, as well as attempts to improve the reaction selectivity, are discussed.