Synthesis of Heterocycles Through Hydrosilylation, Silylformylation, Silylcarbocyclization and Cyclohydrocarbonylation Reactions

Ethylene Transposition: Ruthenium Hydride Catalyzed Intramolecular trans-Silylvinylation of Internal Alkynes

“…The majority of work in this area has focused on hydrosilylation chemistry. − Recently, a number of ruthenium catalyzed protocols have emerged for the synthesis of trisubstituted olefins using an intramolecular hydrosilylation of alkynes. − These complementary routes to trisubstituted vinylsilanes are inherently limited due to the mandatory inclusion of a hydrogen atom into the product alkene. Subsequent studies on silylcarbonylation and silylcyanation of alkynes have been described to circumvent this limitation. − Specifically, Ojima and Denmark have studied the silylformylation of alkynes and found that five- and six-membered rings could be formed readily in this reaction. − Silylformylation and silylcyanation reactions afford the syn -alkene isomers selectively. Intermolecular versions of silylcarbocyclization reactions also afford the syn -isomers. − We have recently reported that vinyl-silicon tethers can be used to control both the regio- and stereochemistry in the silylvinylation of pendent alkynes with acrylates …”

B(C6F5)3-Promoted Tandem Silylation and Intramolecular Hydrosilylation: Diastereoselective Synthesis of Oxasilinanes and Oxasilepanes

“…Although 5- exo cyclizations are well-established for Pt-or Rh-catalyzed hydrosilylations,1,3 we observed selective 6- endo vs. 5- exo cyclization with a substrate where either mode would proceed via a secondary carbocation (Table 2, substrate 11 ). We also observed very different rates for 6- exo and 6- endo cyclizations involving electronically similar carbocation intermediates ( 7-Pr vs. 1-Pr ).…”

“…These results point to the importance of interactions between the alkene and the developing silylium-like species. The cis selectivity observed for six-membered ring annelations, which complements results from metal-catalyzed cyclizations,1,3,22 presumably reflects stereoelectronic requirements for trapping of the β-silyl cations 23. The stereoselectivity of sidechain introduction results from cyclization through the low-energy conformer of a chair-like transition state (eq 1).…”

“…4,5 The majority of examples involve metal-catalyzed 5-endo or 5-exo ring closures, although six-membered cyclizations have been reported. 1,3,6 We now report regio-and stereoselective formation of oxasilinanes and oxasilepanes via formation and cyclization of unsaturated alkoxysilanes in the presence of a nonmetal catalyst.In the course of investigations into the influence of Lewis acids on the ozonolysis of unsaturated silanes, we found that addition of B(C 6 F 5 ) 3 to a solution of unsaturated alkoxysilane 1-Pr resulted in regioselective formation of oxasilinane 2-Pr with high 3,5-trans diastereoselectivity (Table 1). 7,8 The cyclization proceeded efficiently at -78 °C or rt and in the presence of either stoichiometric or catalytic B(C 6 F 5 ) 3 .…”

“…Initially investigated for unsaturated silanes,2 the methodology is now often applied to unsaturated alkoxy- and aminosilanes,3 where stereospecific oxidative cleavage of the newly formed C-Si bond enables stereodefined synthesis of diols and aminoalcohols 4,5. The majority of examples involve metal-catalyzed 5- endo or 5- exo ring closures, although six-membered cyclizations have been reported 1,3,6. We now report regio- and stereoselective formation of oxasilinanes and oxasilepanes via formation and cyclization of unsaturated alkoxysilanes in the presence of a nonmetal catalyst.…”