Alkyl 2-alkynoates, preparation

J.A. Katzenellenbogen et al. developed an efficient method for the synthesis of alkyl-substituted enol lactones that are potent inhibitors of the serine protease elastase. The precursors for the enol lactones were a- and 3-alkyl-substituted 5-hexynoic acids, which were prepared by the bromoform reaction of the corresponding alkynoic methyl... 

In the last example, cis-carbocupration of alkynoic ester 14 provides a weakly nucleophilic and configurationally imstable 1-alkoxycarbonyl alkenylcopper intermediate (15) the presence of HMPA as additive was crucial to avoid erosion of the E/Z stereoselectivity in the alkylation step with electrophile 16 [39, 40]. Under these conditions, 3,3-disubstituted allylboronates 17 were prepared in over 20 1 selectivity, and these reagents were subsequently employed in the stereoselective preparation of quaternary carbon centers (Section 6.4.2.2). 

A stereoselective preparation of functionalized alkyl 2-alkynoates via an Rh(II)-catalysed reaction of silyl enol ethers and 3-siloxy-2-diazobutenoates has been reported (Scheme A1) > 0... 

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