BF3-mediated addition of lithium phenylacetylide to an imine:: Correlations of structures and reactivities.: BF3•R3N derivatives as substitutes for BF3•Et2O

BF3-mediated additions of lithium phenylacetylide (PhCCLi) to the N-(n-butyl)imine of cyclohexane carboxaldehyde were investigated. IR spectroscopic investigations reveal dramatic aging effects on the addition rates. Li-6. B-11, and C-13 NMR spectroscopic studies correlate the loss in reactivity with the condensation of PhCCLi and BS and the consequent formation of a complex mixture of PhCCLi-BF3 adducts. Employing BF3.R3N complexes eliminates the aging effects by retarding the formation of berates. Kinetic studies implicate a mechanism in which rate-limiting associative substitution of n-Bu3N on the BF3 by the imine is followed by a rapid 1,2-addition of PhCCLi. BF3.R3N complexes are potentially useful substitutes for BF3.Et2O.