POLYLITHIUMORGANIC COMPOUNDS .19. REGIOSELECTIVE CARBON-CARBON ALPHA-BOND SCISSION FOLLOWED BY A 1,6-PROTON SHIFT UPON THE REDUCTIVE METALATION OF BENZYLIDENECYCLOPROPANE DERIVATIVES WITH LITHIUM METAL

Depending on the substituent, alpha-substituted benzylidenecyclopropan es (32) react more or less readily with lithium dust (2% sodium) in di ethyl ether whereby a regioselective scission of only the cyclopropane sigma-bond cis to the phenyl ring takes place. Upon raising the tempe rature the primarily formed 1,3-dilithiumorganic compound due to an ag ostic interaction rearranges by a 1,6-proton shift into a doubly bridg ed 1,4-dilithio compound. With alpha-methylbenzylidenecyclopropane (32 c) this rearrangement was shown to occur intermolecularly via a trilit hiumorganic compound 56. The suggested mechanism of these reductive me talation reactions via a bisected radical anion 87 where the lithium i s mainly bound to the cyclopropyl carbon atom and oriented syn to the phenyl ring, was supported by MNDO (geometries) and ab initio (energie s) calculations.