Allylic barium reagents coupling

Homo- and cross-coupling reactions of allyhc halides and reactions of conjugated dienes with dichloroalkanes using reactive barium are reviewed in Section 5.2. The next section covers methods of generating allylic barium reagents and reactions of these carbanions with a variety of electrophiles. The last section describes examples of other carbon-carbon bond forming reactions promoted by barium compounds. 

Allylic barium reagents prepared in this way can realize highly a-selective reactions with different electrophiles, e.g. cross-coupling reactions with allylic halides or allylic phosphates, additions to carbonyl compounds or imines, and ring opening of epoxides. A selective Michael addition reaction with an a,/ -unsaturated cy-cloalkanone can also be performed by use of an allylic barium reagent. 

Corey and coworkers successfully applied this cross-coupling method to the synthesis of (3S)-2,3-oxidosqualene (Scheme 10.2 5) [3]. The utility of allylic barium reagents for nucleophilic substitution reactions was further demonstrated by the synthesis of cembrol A (7), in which ring closure of the epoxy compound occurred regioselectively (Scheme 10.3) [4]. 

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