Organolithium compounds conjugate additions

Organolithium compounds are highly reactive and have been used in a variety of organic transformations. A major problem in the development of catalytic asymmetric conjugate additions of organolithium reagents to a,/3-unsaturated carbonyl compounds is that the high reactivity of RLi may cause both low chemoselectivity (1,2- vs. 1,4-addition) and low enantioselectivity. 

The chemical behavior of heteroatom-substituted vinylcarbene complexes is similar to that of a,(3-unsaturated carbonyl compounds (Figure 2.17) [206]. It is possible to perform Michael additions [217,230], 1,4-addition of cuprates [151], additions of nucleophilic radicals [231], 1,3-dipolar cycloadditions [232,233], inter-[234-241] or intramolecular [220,242] Diels-Alder reactions, as well as Simmons-Smith- [243], sulfur ylide- [244] or diazomethane-mediated [151] cyclopropanati-ons of the vinylcarbene C-C double bond. The treatment of arylcarbene complexes with organolithium reagents ean lead via conjugate addition to substituted 1,4-cyclohexadien-6-ylidene complexes [245]. 

Alkenyl trityl ketones, prepared by reaction of 1 with a ketone followed by dehydration, undergo exclusive conjugate addition on reaction with organolithium compounds. The adducts are cleaved to primary alcohols on reduction with LiB(C2H5)3H. 

Nucleophilic addition to styrene is possible only because the intermediate carbanion is stabilized by conjugation into the benzene ring. It needs a more reactive carbanion than the benzyl anion to initiate the polymerization, and an unstabilized nonconjugated organolithium compound like butyl lithium is the answer. 

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