Silylacetylenes Trimethylsilylacetylenes

Glycals serve as activated sugars because of the inherent reactivity of the endocyclic enol ether. Consequently, they have been extremely useful substrates in their complementarity to native activated sugars. Additionally, they have been used to demonstrate versatility not directly available from other sugar derivatives. In a good example of the utility of allylsilanes and silylacetylenes in C-glycoside chemistry, Ichikawa et al. [91] demonstrated a preference for the a anomer in all cases. The results, shown in Scheme 7.17, included a demonstration that a characteristic nOe can be used to confirm the stereochemical outcome of the reaction with hw-trimethylsilylacetylene. 

Addition of silylacetylenes to carbonyl compounds This salt catalyzes the addition of l-phenyl-2-trimethylsilylacetylene (1) to aldehydes or ketones at room temperature to form adducts which can be isolated in the silylated form (2) or as alcohols (3). The reaction of (a) with ,)S-unsaturated carbonyl compounds is generally not useful. See Ethyl trimethylsilylacelate-Tetra-ii-butylannnoniani fluoride, this volume. 

Another example of Pd(0)-catalyzed dimerizations of alkynes was reported by Ishikawa and co-workers. Terminal silylacetylenes 19, containing at least one phenyl group at the silyl moiety, in the presence of Pd(PPh3)4 underwent homodimerization in a head-to-head fashion to produce the corresponding bis-silylenynes 20 in reasonable yields (Scheme 7). The preferred anti-Markovnikov-type regiochemistry in these cases and also in the Pd(+2)-catalyzed homodimerization of trimethylsilylacetylene was explained with steric factors. ... 

Trimethylsilyl-3-rnethylthio-l-propyne, 54 - (32) Trimethyl-silylacetylene, 55 - (32) Bis(trimethylsilyl)acetylene, 56 - (33) 1--Ethoxy-2-trimethylsilylacetylene, 57 - (34) 3-Trimethylsilyl-2 -propyn--l-ol, 58 - (35) 2-Butynoic acid, 59 - (3S) Methyl-1-propynyl sulfoxide,... 

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