Cyclopropenes carbocupration

In the addition of Me2CuLi reagents to electron-deficient acetylenes [85-88], DCD-type complexes have been identified by NMR [84, 89]. As shown below, an ynoate affords a vinylcopper intermediate, while an ynone instead affords an allenolate (Eq. 10.9). The origin of this diversity remains unclear. A related carbocupration mechanism has also been proposed for the reaction with allenylphosphme oxide [53]. Olefin carbocupration of dienes [90] and cyclopropenes [34, 36] is known, but these mechanisms also remain unclear. 

Finally, the carbometallation reaction of spirocyclic cyclopropenes with a chiral ketal attached to the substrate was described. Thus, carbocupration of the chiral cyclopropene 96 proceeded with 96% diastereoselectivity with a higher-order organocuprate [134] (Scheme 7-114). 

The carbocupration of cyclopropenes has been especially investigated with cyclopropenone ketals as reactants. The cuprio cyclopropanes formed can serve as a synthon for the cyclo-propanone enolate. " Achiral ketals with an unsubstituted cyclopropene double bond 15 undergo instantaneous reaction with lithium dimethylcuprate at — 78 C to give the methyl derivative 17 (R = Me) in 96% yield after quenching with methanol. Similar reactions, with a deuterium oxide or iodomethane quench, indicate that the carbocupration takes place in a cis fashion. 

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