Carboalumination Organoaluminium chemistry

organoaluminum compounds can react alkenes , alkynes, resulting in net addition of 1 organyl group , metal fragment across multiple bond (carboalumination). process can proceed in purely thermal manner or in presence of transition metal catalyst. uncatalyzed process, monoaddition possible when alkene substituted. ethylene, carboalumination leads poisson distribution of higher alkylaluminum species. reaction regioselective 1-alkenes. so-called zaca reaction first reported e.-i. negishi example of asymmetric carboalumination of alkenes catalyzed chiral zirconocene catalyst.

the methylalumination of alkynes in presence of cp2zrcl2 employed synthesis of stereodefined trisubstituted olefin fragments, common substructure in terpene , polyketide natural products. synthesis of (e)-4-iodo-3-methylbut-3-en-1-ol shown below typical application of reaction:

for terminal alkynes, reaction proceeds regioselectivity (>90:10 rr) , complete syn selectivity, in presence of propargylic or homopropargylic heteroatom substituents. unfortunately, extension of zirconocene-catalyzed methylalumination alkylalumination higher alkyls results in lower yields , poor regioselectivities.