Carba-Michael additions

Several other asymmetric inter- as well intramolecular Friedel-Crafts alkylation with a,(3-unsaturated aldehydes have been described but without any configurative assignment [91]. Asymmetric carba-Michael additions of aldehydes to enones catalyzed by a chiral imidazolidin-4-one were reported by GeUman et al. [8] (Scheme 4.23). 

A 2,2-disubstituted chromane system was asymmetrically constructed by application of intramolecular oxa-Michael addition reaction through 6-exo-trig mode cyclization [57]. Good asymmetric induction at the quaternary carbon was observed when Z-alkene was treated with the same guanidine 17 used in asymmetric carba-Michael reaction in Table 4.5 (Scheme 4.18). 

Investigation of the Michael addition reaction of phosphonate carba-nions to a-nitroalkenes revealed that diethyl ether, used either as an achiral additive for the cinchonine or a mixture of cinchonine/cinchonidine catalysts or as a solvent, delivered different stereoisomers of y-nitroalkylpho-sphonates (203) than in THF, often with a reversal of enantioselectivity (Scheme 71). ... 

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