Silicon synthesis from alkynes

Skrydstrup, Beau and co-workers122 have adapted Stork s method to the SmI2-reduction of glycosyl pyridyl sulfones bearing a silicon-tethered unsaturated group at HO-C(2). An example is shown with the synthesis of methyl a-C-zso-maltoside 172 from alkyne 170 via the 5-exo-dig radical cyclization of 171 (Scheme 56).144... 

Our strategy for the Smij-promoted synthesis of l,2-cis-C-glycosides is illustrated in Figure 3. It was assumed that one-electron transfer to the LUMO of the aryl sulfone group in A would result in concomitant cleavage of the C1 -S bond liberating an anomeric radical intermediate, as previously observed in the reductive lithiation of glycosyl phenyl sulfones." If 5-exo cyclization onto the silicon-tethered alkene/alkyne is substantially favored over a second electron transfer from Smij, then the exocyclic carbon radical B would ultimately be formed. On the other hand, reduction of the Cl-radical by... 

Summary Cl2Si=CHCH2/Bu is a versatile building block in organosilicon synthesis which reacts with a wide variety of multiple bond systems. The unique reactivity is shown by the predominance of [2+2] over [4+2] cycloaddition reactions. This unusual behaviour is caused by the two chlorine substituents at the silicon atom. This presentation shows the synthesis of silacyclobutenes from Cl2Si=CHCH2tBu and disubstituted alkynes and some chemistry of these four membered ring compotmds. 

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