AN UNEXPECTED 1,2-ALKYL SHIFT WITHIN A CHELATE BONDED ORGANOALUMINUM-ENAMINE

The organozinc-enamines EtZn[R'N-CH=CH-N(Et)R'] (R=(t)Bu (1a), (t)pent (2a), (i)Pr (3a)) react with Et3Al via a transmetallation reaction to the corresponding organoaluminium-enamines Et2Al[R'N-CH=CH-N(Et)R'] ( R'=(t)Bu (1c), (t)pent (2c)) and Et2Zn. Prior to the transmetallation reaction initial 1 : 1 zinc-enamine-trialkylaluminium adducts are form ed. Compounds 1c and 2c are thermally unstable and rearrange via a 1,2 -alkyl shift partly in combination with a hydrogen shift, to Et2Al[R'N =CH-C(H)R'-NEt] (R'=(t)Bu (1d), (t)pent (2d)) (70%) and Et2Al[R'N-CH2C R'=NEt] (R'=(t)Bu (1e), (t)pent (2e)) (30%). The driving force for the alkyl shift, which is restricted to tertiary alkyl groups, is release of steric strain in the five-membered NCCN aluminium chelate ring.