An Unexpected 1,2-Alkyl Shift within a Chelate Bonded Organo-Aluminum-Enamine

Abstract

The organozinc-enamines EtZn[R’N-CH=CH-N(Et)R’] (R =‘Bu (la), ‘pent (2a), ‘Pr (3a)) react with Et,Al via a transmetallation reaction to the corresponding organoaluminium-enamines Et,Af[R’N-CH=CH-N(Et)R’l (R’ =‘Bu (1~1, ‘pent (2~)) and EtzZn. Prior to the transmetallation reaction initial 1: 1 zinc-enamine-trialkylaluminium adducts are formed. Compounds lc and tc are thermally unstable and rearrange via a 1,Zalkyl shift partly in combination with a hydrogen shift, to EtzAl[R’N=CH-C(H)R’-NEtl (R’ =‘Bu (la), ‘pent (2d)) (70%) and Et,Al[R’N-CH,CR’=NEtl (R’ =‘Bu (le), ‘pent (2e)) (30%). The driving force for the alltyl shift, which is restricted to tertiary alkyl groups, is release of steric strain in the five-membered NCCN aluminium chelate ring.