INTRAMOLECULAR ADDITION OF ALKYLLITHIUMS TO ACETYLENES - REGIOSPECIFIC 4-EXO-DIG, 5-EXO-DIG, AND 6-EXO-DIG CYCLIZATIONS

Primary acetylenic alkyllithiums bearing a phenyl substituent on the triple bond, which may be prepared in virtually quantitative yield by low-temperature lithium-iodine interchange, undergo regiospecific exo-dig cyclization via stereoselective syn-addition of CH2Li to the carbon-carbon triple bond to give four-, five-, and six-membered carbocycles bearing an easily functionalized exocyclic lithiomethylidene moiety. Cyclization of the analogous alkyl substituted acetylenic alkyllithiums is confined to the 5-exo-dig mode. © 1990.