%0 Journal Article
%T Intramolecular carbolithiation cascades as a route to a highly strained carbocyclic framework: competition between 5-exo-trig ring closure and proton transfer
%A William F. Bailey
%A Justin D. Fair
%J Beilstein Journal of Organic Chemistry
%D 2013
%I 
%R 10.3762/bjoc.9.59
%X The preparation of fairly strained carbocyclic ring systems by intramolecular 5-exo-trig ring closure has been well documented, and the absence of proton transfers that would compromise such cyclizations is a hallmark of this chemistry. In an effort to explore the limitations of this approach to more highly strained systems, the preparation of a stellane (tricyclo[3.3.0.03,7]octane) framework by an intramolecular carbolithiation cascade involving three coupled 5-exo-trig cyclizations of the vinyllithium derived from 2-bromo-4-vinyl-1,6-heptadiene by lithium¨Cbromine exchange was investigated. The cascade does not afford the stellane; rather, the cascade is terminated after two cyclizations by a proton transfer that occurs by an intermolecular process catalyzed by trace amounts of endo-5-methyl-2-methylenebicyclo[2.2.1]heptane present in reaction mixtures as a consequence of inadvertent quenching of an intermediate alkyllithium during prolonged reaction times at room temperature.
%K carbolithiation cascade
%K carbometallation
%K intramolecular carbolithiation
%K intermolecular proton transfer
%K lithium¨Chalogen exchange
%K strained hydrocarbons
%U http://dx.doi.org/10.3762/bjoc.9.59