Asymmetric Hydrovinylation of 1-Vinylcycloalkenes. Reagent Control of Regio- and Stereoselectivity

摘要

1-Vinylcycloalkenes undergo highly regio-and enantioselective (>98% ee) 1,4-hydrovinylation (HV) when treated with ethylene (1 atm) at room temperature in the presence of [(S,S)-2,4-Hs-diphenylphosphinopen-tane (BDPP)]CoCl_2 (0.05 equiv) and methylaluminoxane. The minor 1,2-HV products, seen only in 1-vinyl -cyclohexene (～15%) and 1-vinylcycloheptene (2%), are formed as racemic mixtures. The corresponding Ni(Ⅱ)-catalyzed HV reactions of these substrates give mostly the 1,2-adducts. Racemic 4-tert-butyl-l-vinylcyclohexene, when treated with Co[(S,S)-(BDPP)]Cl_2 and ethylene, undergoes a rare enantiodivergent reaction giving two diastereomers each in >98% ee.