Cyclohexene hydroalumination

The hydroalumination of cycloalkenes exhibits two interesting minima in relative rates toward diethyl-aluminum hydride. The half-life (in min) of a 3 1 ratio of Et2AlH and cycloalkene at 78 °C varied thus with ring size C4, 40 C5, 200 Ce, 1880 C7, 110 Cg, 86 C9, 280 Cio, 2500 Cn, 1350. The reactivity of cycloundecene is approximately that of an open-chain internal alkene. The low reactivity of cyclohexene can be ascribed to the eclipsing repulsions generated in the transition state by the syn attack of Et2AlH on the C=C bond (equation 17). ... 

The nickel-catalyzed hydroalumination of alkenes has been extensively investigated in a variety of contexts. The interaction of aluminum hydrides with nickel(0) and the mechanism of alkene hydroalumination has been studied in detail by Wilke, Eisch, and Zweifel. The most extensive synthetic applications from Lautens involve the hydroalumination of oxabicyclic alkenes followed by ring opening to produce substituted cyclohexenes and cycloheptenes (Scheme 74). - An as5mimetric variant emplo5dng 2,2 -bis(diphenylphosphino)-l,l -binaphthyl (BINAP) is also quite general for various oxabicyclic starting materials. 

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