CARBANIONS-27 - REARRANGEMENTS OF (9-ALKYL-9-FLUORENYL)METHYLLITHIUM (OR CESIUM) AND 2,2-DIPHENYL-3,3-DIMETHYLBUTYLLITHIUM

A study has been made upon the products from warming various (9-alkyl- 9-fluorenyl)methyllithium (or cesium) compounds in THF to near 0 degre es C followed by carbonation. When the 9-alkyl group is ethyl, the res ult is chiefly the protonated product (9-alkyl-9-fluorenyl)methane; a similar product evidently is formed when the 9-alkyl group is 1-norbor nyl. When the 9-alkyl group is tert-butyl, the minor product is 9-neop entylfluorene-9-carboxylic acid from a [1,2]-migration of the tert-but yl group while the major product is 9-methylfluorene-9-carboxylic acid from an intramolecular elimination as shown by deuterium labeling. Wh en the 9-alkyl is neopentyl, the major product is 9-neopentyl-9,10-dih ydrophenanthrene-9-carboxylic acid along with some 9-neopentylphenanth rene which becomes the major product in diethyl ether solution at 35 d egrees C. 2,2-Diphenyl-3,3-dimethylbutyllithium undergoes predominantl y [1,2]-phenyl migration in THF at 0 degrees C. From an x-ray crystal study upon 9-tert-butyl-9-(chloromethyl) fluorene and 9-neopentyl-9-(c hloromethyl)fluorene, it is concluded that steric acceleration is resp onsible for the unusual reactions of (9-alkyl-9-fluorenyl)methyllithiu ms when the 9-alkyl groups are tert-butyl and neopentyl.