Radical Addition of RCHO, ACOX and Related Compounds to Alkenes

3 Radical Addition of RCHO, ACOX and Related Compounds to Alkenes 

It has long been known that unsymmetrical ketones can be prepared by the reaction of aldehydes with alkenes under free-radical reaction conditions. Recently the revision of this chemistry has been reported by the Roberts group [42], They introduced thiols as a polarity reversal catalyst for the addition of aldehydes to alkenes. Thiyl radicals are electrophilic, and therefore a polar Sh2 type transition state for the hydrogen transfer step from an aldehyde would be ideal in this situation. Indeed, the addition of aldehydes to a variety of alkenes can be effected by 

Fuchs and Gong reported an acyl radical transfer reaction from aldehydes to acetylenic trifluoromethylsulfones to give acetylenic ketones [43J. In this case, tri-fluoromethyl radical, arising from the a-scission of trifluoromethylsulfonyl radical, abstracts the hydrogen of an aldehyde to form an acyl radical, which then propagates the chain. 

Acyl radical sources, other than aldehydes, are also available. The group transfer addition of an acyl radical has been reported by Zard and co-workers, where S-acyl xanthates serve as acyl radical sources [44]. Crich and co-workers reported that an acyl radical, generated from an aromatic acyl telluride by photolysis, adds to an allylic sulfide which contains an ethoxycarbonyl group to form the corre-.sponding y-unsaturated ketones [45]. The addition pathway involves Sh2 type reaction with extrusion of a /ert-butylthiyl radical. 

Curran and Schwarz determined the optimal conditions for a similar acyl radical transfer reaction from acyl methyl selenide to methyl acrylate to achieve the 

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