Diolefinic alkyllithiums

The historical development of alkyllithium-initiated polymerization of olefins and diolefins for the synthesis of elastomeric materials is of interest not only because of its scientific and technological significance but also because of the insight it provides into the thinking and methodology of polymer (elastomer) researchers. 

The stereocontrol inherent in the totally regiospecific 5-exo-trig isomerizations of substituted 5-hexenyllithiums may be exploited for the stereoselective synthesis of bicyclic systems by tandem cyclization of acyclic diolefinic alkyllithiums. To date, this strategy has not been widely applied, and the first examples were reported by Bailey and Rossi who were able to cyclize the organolithiums derived from iodides 113 and 115 in the presence of TMEDA to afford the polycarbocyclic products 114 and 116 (Scheme 33)61. 

The regiospecific 5-exo-trig cyclizations of substituted 5-hexenyllithiums was exploited for the stereoselective synthesis of bicyclic systems by tandem cyclization of acyclic diolefinic alkyllithiums [42]. However, this carbocycle synthesis has three major limitations ... 

In either method alkyllithiums are the standard initiators employed. Sec-Butyllithium (s-BuLi) is frequently used because its rate of addition to styrene or conjugated diolefins is very fast. In Reaction la there are essentially three initiation steps, or more precisely one initiation and two crossover steps. 

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See also in sourсe #XX -- [ ]

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