Vicinal difunctionalization nucleophiles

The two distinct bond-forming steps in tandem vicinal difunctionalization have been studied extensively. The first step consists of a nucleophilic addition to a ir-system the nucleophile is almost invariably an organometal. 1,4-Addition to an a, -unsaturated carbonyl substrate concomitantly generates a new cr-bond at the (3-carbon and an enolate ion. The second step constitutes C-functionalization of the enolate intermediate, forming a new o -bond between the nucleophilic a-carbon of the enolate and an electrophilic reagent. 

A similar but conceptually distinct approach to difunctionalization of terminal alkynes consists of sequential carboboration-palladium-catalyzed cross-coupling 137 equation (33) illustrates that this method also provides alkenes of high stereochemical purity by net syn Markovnikov addition. Benzyne-contain-ing molecules can act as highly activated substrates for vicinal difunctionalizations initiated by nucleophiles 138-140 thus, nucleophilic addition-electrophilic trapping can serve as an alternative to sequential directed metallation for the production of 1,2-disubstituted and 1,2,3-trisubstituted aromatic systems (equation 34).141... 

A wide range of nucleophilic reagents has been used to initiate tandem vicinal difunctionalizations of a, -un saturated carbonyl-containing substrates. Dominant among these reagents are organocopper (Gil-... 

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