Cyclization by intramolecular carbolithiation of alkyl- and vinyllithiums prepared by reductive lithiation: surprising stereochemistry in the lithium oxyanion accelerated cyclization.
The versatility of intramolecular carbolithiation of simple alkenes to yield cyclopentylmethyllithiums by unconjugated organolithiums is greatly increased (1) by generating the organolithiums by reductive lithiation of phenyl thioethers with aromatic radical anions and (2) by using allylic or homoallylic alcohol groups on the receiving alkene. This type of reductive lithiation allows virtually any kind of organolithium to be generated, usually in a connective manner. Furthermore, the allylic or homoallylic lithium oxyanionic groups on the alkene greatly accelerate the reactions and lead in most cases to completely stereoselective cyclization at -78 degrees . Most significantly, the trans stereoselectivity is the opposite from that observed when the organometallic is allylic. A four-membered ring has also been generated by this method.
Deng
Kai
K
Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA.
Bensari
Ahlem
A
Cohen
Theodore
T