Hydrosilylation disubstituted alkynes

In the same manner, the Pt-catalyzed intramolecular hydrosilylation of disubstituted alkyne, < -dimethylsiloxyalkynes 127, derived from alkynols 126, affords E configuration of 5-exo-alkylidene-2-oxasilacyclopentanes 128, which serves as useful intermediates for further functionalizations (Scheme 62) (112). 

In analogy with the strategy of carbocyclic construction, 1,6-enynes containing an oxygen heteroatom in the carbon atom sequence have been used for 3,4-disubstituted tetrahydrofuran synthesis. The simplest example is given by the hydrosilylation of enyne at room temperature (Reaction 7.38) [49]. Tetrahydrofurans with an exocyclic methylene functionality can also be prepared from the appropriate alkynes, such as 32, with (TMS)3SiH in refluxing benzene which afforded exclusive formation of the exomethylene in the Z conformation (Reaction 7.39) [50]. 

Shibata and co-workers have reported an effective protocol for the cyclization/hydrosilylation of functionalized eneallenes catalyzed by mononuclear rhodium carbonyl complexes.For example, reaction of tosylamide 13 (X = NTs, R = Me) with triethoxysilane catalyzed by Rh(acac)(GO)2 in toluene at 60 °G gave protected pyrrolidine 14 in 82% yield with >20 1 diastereoselectivity and with exclusive delivery of the silane to the G=G bond of the eneallene (Equation (10)). Whereas trimethoxysilane gave results comparable to those obtained with triethoxysilane, employment of dimethylphenylsilane or a trialkylsilane led to significantly diminished yields of 14. Although effective rhodium-catalyzed cyclization/hydrosilylation was restricted to eneallenes that possessed terminal disubstitution of the allene moiety, the protocol tolerated both alkyl and aryl substitution on the terminal alkyne carbon atom and was applicable to the synthesis of cyclopentanes, pyrrolidines, and tetrahydrofurans (Equation (10)). 

Hydrosilylation of alkenes and alkynes This reaction can be effected with 1 and an initiator at 90°. Reaction with monosubslituted and gem-disubstituted alkenes shows high a f/-Markovnikov rcgioselcctivity. cis- or fram-Disubstituted and trisubslituted alkenes are hydrosilylatcd in high yield but require longer reaction times. 

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