Alkenes divinyl ketones from

Friedel-Crafts acylation of alkenes (Daizens-Nenitzescu reaction ) with unsaturated acylium ions generated from acid halides and Lewis acids constitutes a general synthesis of divinyl ketones. 

Nitrogen can be incorporated as an oxime into a different kind of ene reaction that has been explored by Grigg and his group. The ene component now bears no resemblance to a diene one pair of electrons comes from the lone pair on nitrogen and the other from the OH bond of the oxime 140. The enophile is a more conventional enone and the initial product is a nitrone 141. No nitrogen heterocycle is formed in this step, but, if the enophile contains a second alkene, a 1,3-dipolar cycloaddition gives a bicyclic structure. The simplest reagent for this job is the rather unstable divinyl ketone (penta-l,4-dien-3-one, 143). Fortunately this can be released from the dichloroketone 142 with base and distilled with the solvent THF into the reaction mixture.24... 

In 1998, the first deliberate attempt to trap the oxyallyl cation with a nucleophile during a thermal Nazarov reaction was reported by West and coworkers [23]. Coining the term interrupted Nazarov reaction, they described the interception of the oxyallyl intermediate of a Nazarov reaction by a tethered alkene (Scheme 3.20). Upon submission of divinyl ketones 87 to the LA, a conrotatory ring closure generates the oxyallyl cation intermediate 89. The alkene moiety adds selectively to the oxyallyl cation intermediate to form bicycle 90. The stabilized tertiary carbocation is then trapped by the enolate oxygen to give intermediate 91, which, under acidic aqueous conditions, is converted to the final hemiketal product 88. The reaction provides an efficient and stereoselective method to prepare tricychc compounds 88 in yields ranging from 42 to 89% [24]. 

Parrain and coworkers described an efficient cascade involving the ring opening of cyclopropene ketal of type 71 followed by CM with a variety of alkenes in the presence of catalyst [Ru]-I for the synthesis of protected divinyl ketones [42]. This sequence was employed by Kozmin and coworkers for the preparation of the linear center portion of bistramide A, a marine metabolite isolated from Lissodinum bistratum which exhibits potent cytotoxicity against several cell lines [43], as well as... 

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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