Alkynes divinyl ketones from

Cyclization of Divinyl Ketones from Alkynic Alcohols... 

A usefid feature of the Nazarov cyclization is the construction of fused bicyclic systems by annulation of a flve-membered ring. This requires one of the vinyl groups to be embedded in a ring. These precursors can be formed easily by vinyl alkyne addition to cyclic ketones followed by dehydration and hydrolysis. This procedure woiks well for symmetrical ketones but it gives regioisomers from unsymmetrical ketones such as 1- or 2-octalone."- A superior method, reported by Paquette, 76 involves the acylation of cycloalkenylsilanes to provide divinyl ketones (equation 6). The advantages of this protocol are discussed in Section 6.3.7.4.3. 

The hydrosi(ly)lations of alkenes and alkynes are very important catalytic processes for the synthesis of alkyl- and alkenyl-silanes, respectively, which can be further transformed into aldehydes, ketones or alcohols by estabhshed stoichiometric organic transformations, or used as nucleophiles in cross-coupling reactions. Hydrosilylation is also used for the derivatisation of Si containing polymers. The drawbacks of the most widespread hydrosilylation catalysts [the Speier s system, H PtCl/PrOH, and Karstedt s complex [Pt2(divinyl-disiloxane)3] include the formation of side-products, in addition to the desired anh-Markovnikov Si-H addition product. In the hydrosilylation of alkynes, formation of di-silanes (by competing further reaction of the product alkenyl-silane) and of geometrical isomers (a-isomer from the Markovnikov addition and Z-p and -P from the anh-Markovnikov addition. Scheme 2.6) are also possible. 

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