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An unexpected 1,2-alkyl shift within a chelate bonded organoaluminium-enamine

1993; Elsevier BV; Volume: 459; Issue: 1-2 Linguagem: Inglês

10.1016/0022-328x(93)86050-r

1872-8561

Elmo Wissing, Johann T. B. H. Jastrzebski, Jaap Boersma, Gerard van Koten,

Organometallic Complex Synthesis and Catalysis

The organozinc-enamines EtZn[R′NCHCHN(Et)R′] (R  tBu (1a), tpent (2a),iPr (3a)) react with Et3Al via a transmetallation reaction to the corresponding organoaluminium-enamines Et2Al[R′NCH CHN(Et)R′] (R′ tBu (1c), tpent (2c)) and Et2Zn. Prior to the transmetallation reaction initial 1:1 zinc-enamine-trialkylaluminium adducts are formed. 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′ tBu (1d), tpent (2d)) (70%) and Et2Al[R′NCH2CR′NEt] (R′ tBu (1e), tpent (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.