The Stereochemistry of the Addition of Silicochloroform to Acetylenes. A Comparison of Catalyst Systems

Synthesis of Vinylsilanes

“…The use of platinum catalysts in alkyne hydrosilylation originated with Benkeser's 6 and Lewis' 7 discovery that Speier's (H 2 PtCl 6 ) and Karstedt's [Pt 2 (DVDS) 3 ] catalysts could achieve good selectivity in the syn-hydrosilylation of terminal alkynes, as exemplified by hept-1-yne ( Table 1, entries 1-7). 7,8 The use of bulky phosphine ligands improves both the stereo-and regioselectivity of this process for the formation of (E)-vinylsilanes (e.g., entries 8-10).…”

Vinylsilanes

“…An alternative route 10 to 1,2-disilylethenes is the palladium(0)-catalysed addition-elimination sequence shown in Scheme 7.7, the (£)-alkene giving the (£>disilylethene (3).…”

“…(Me 3 Si) 3 Aldehyde substrates react smoothly to produce vinylsilanes as (Z,£)-mixtures (Scheme 7.26); yields are, however, rather poor if the aldehyde is enolizable. Ketones, on the other hand, must be non-enolizable to be of any utility; here, stereoselectivity has been determined in only one case, that of t-butyl phenyl ketone, when the isomer (15) was sole product, presumably because of the greater eclipsing interactions in the alternative rotamer (16) (Scheme 7.27).…”

“…The silylated methyl vinyl ketone (35) successfully traps 3 (36) is relatively stable (Chapter 2), and is therefore less basic than the starting enolate (37). Under such reaction conditions, extensive polymerization of the vinyl ketone takes place, as do relatively rapid proton transfer reactions, resulting in loss of enolate regiospecificity.…”

Silanes as reducing agents

“…Under such conditions, alkynes undergo as-addition 5 , 6 (Scheme 27./), and so provide one of the major routes to vinylsilanes (Chapter 7). Peroxide-initiated addition 5 , on the other hand, gives mainly the products of taws-addition, whereas nickel(II) catalyses 7 a stereoselective double c/s-addition (Scheme 21.1).…”