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

BF3-mediated additions of lithium phenylacetylide (PhCCLi) to the N-(n-buty l)imine of cyclohexane carboxaldehyde were investigated. IR spectroscopic i nvestigations reveal dramatic aging effects on the addition rates. Li-6. B- 11, and C-13 NMR spectroscopic studies correlate the loss in reactivity wit h the condensation of PhCCLi and BS and the consequent formation of a compl ex mixture of PhCCLi-BF3 adducts. Employing BF3.R3N complexes eliminates th e aging effects by retarding the formation of berates. Kinetic studies impl icate 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.