Carbanion-mediated conjugate additions

Other researchers had encountered related problems in attempting to link C14 to C21 via carbanion-mediated conjugate additions. Stork and co-workers reported a successful transformation of iodide 55 to ABDEF... 

The cerium(III)-mediated conjugate addition of a difluoromethylphosphonate carbanion to a wide range of aliphatic nitroalkenes,acyclic and cyclic vinyl sulfones,5 and vinyl sulfoxides has been reported recently (Scheme 3.85). 

Lequeux, T.P., and Percy, J.M., Ceriiun-mediated conjugate additions of a difluorophosphonate carbanion to nitroalkenes, Synlett, 361, 1995. 

Mesylation of the alcohol 65 followed by deprotonation afforded the sul-fone-stabilized carbanion 66 that underwent a macrocyclization to afford the artificial dolabellane 67 in moderate yield (Scheme 9). Hydrolytic cleavage of the ketal (67) followed by a base-mediated double bond isomerization (into conjugation) afforded an enone containing an exocyclic carbonyl group. Nucleophilic 1,2-addition of methyl lithium introduced the missing... 

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