Hydrosilation stereoselective reactions

The C—Si bond formed by the hydrosilation of alkene is a stable bond. Although it is difficult to convert the C—Si bond to other functional groups, it can be converted to alcohols by oxidation with MCPBA or H2O2. This reaction enhances the usefulness of hydrosilylation of alkenes [219], Combination of intramolecular hydrosilylation of allylic or homoallylic alcohols and the oxidation offers regio- and stereoselective preparation of diols [220], Internal alkenes are difficult to hydrosilylate without isomerization to terminal alkenes. However, intramolecular hydrosilation of internal alkenes can be carried out without isomerization. Intramolecular hydrosilylation of the silyl ether 572 of the homoallylic alcohol 571 afforded 573 regio- and stereoselectively, and the Prelog-Djerassi lactone 574 was prepared by applying this method. 

The reaction of terminal allyl alcohols proceeds in a 5-endo fashion to give five-membered ring compounds regioselectively and stereoselectively. Subsequent oxidation affords 2,3-5 y -l,3-diols preferentially, regardless of the nature of the catalyst (eq 1). The stereoselectivity increases with increased bulkiness of the al-lylic substituent and the nature of the alkene substituent (see below). 5-Exo type cyclization occurs with homoallyl alcohols to form five-membered heterocycles and 1,3-diols after oxidation. Two chiral centers are produced in this reaction. The 2,3-relationship (anti) is controlled by the allylic substituent, while the 3,4-relationship is determined by the stereochemistry of the alkene the hydrosilation occurs by cis addition of Si-H to the alkene (eq 2). ... 

The intramolecular hydrosilation of homopropargyl alcohols also proceeds in a 5-exo manner to form five-membered cyclic vinylsilanes exclusively. Subsequent oxidation affords a p hydroxy ketone (eq 6). The vinylsilane also undergoes a Pd-catalyzed cross-coupling reaction with aryl or alkenyl halides stereoselectively (eq 6). The intramolecular hydrosilation thus provides an efficient methodology for the regio- and/or stereoselective functionalization and carbon-carbon bond formation of the alkyne moiety in homopropargyl alcohol. 

The ability of Pd complexes to catalyze tandem cyclization-hydrosilation reactions, that could provide a synthetic route to carbocycles of interest in the fields of biochemistry and medicine, was recently demonstrated. Widenhoefer s group has developed phenanthroline-based complexes 11 and others that quite efficiently bring about this dual transformation for a wide variety of functionalized dienes, with high regio- and stereoselectivities [e.g., Eq. (10)]. ... 

Hydrosilylation of multiple bonds has not often been catalyzed by cyclopenta-dienylmetal complexes. Nevertheless, several methods concerning hydrosilylation of terminal and internal alkynes catalyzed by the ruthenium complex 53 and [(/] -C5Me5)Ru(MeCN)3] PF6 70 have been recently reported [36]. Of special interest is the complex 70, which has a high preference for the formation of the branched 71 over the linear product 72 (Scheme 28). The reaction of the Si-H bond with the triple bond is stereoselectively frans-addition. In the case of alkynyl silanes the reaction proceeds through endo-dig hydrosil tion to the silacycles 73 with endocyclic double bond (Scheme 29) [36b]. 

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