Ketene selenoacetals

In the last section, the access to a-selanyl vinylmetals is considered. Besides the classical methods involving vinylic selenides and ketene selenoacetals, the hydrometallation (M = Sn, Zr, B) of acetylenic selenides constitutes an efficient method. These species can be considered as vinyl dianion equivalents. Some examples of cross-coupling reactions are presented. 

Generation from Vinylic Selenides and Ketene Selenoacetals.136... 

In this concluding section, we will recall that a-selanylvinylmetal derivatives can be produced by a-deprotonation of vinylic aryl selenides 11, cleavage of ketene selenoacetals 12 or bromine/lithium exchange of a-bromovinyl selenides 13 (Scheme 49). These strategies involve vinylic selenides whose syntheses are not simple. More recent works have used organocuprate additions, hydrometala-tions (M = Sn, Zr) or hydroborations of readily available acetylenic selenides 14 (Scheme 49). The process can be regio- and stereocontrolled and produce the a-selanylvinylmetal derivatives under mild conditions. The latter can be considered as vinyl dianion equivalents and are very useful intermediates for cross-coupling reactions. 

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