| Part I. Various amine boranes were used in the reduction of substituted cyclic N-diphenylphosphinyl imines to the corresponding N-diphenylphosphinyl amines, which represent protected primary amines. t-Butylamine borane in methanol appeared to be the most efficient amine borane reagent to accomplish diastereoselective reductions. For reductions of 3- and 4-substituted cyclohexyl systems, this reagent showed a strong preference for axial attack to give the equatorial (trans) isomers. Results with 2-substituted cyclohexyl systems varied depending on the substituent, although all showed a preference for the trans isomer. Cyclopentyl and bicyclic imines were attacked from the less sterically hindered face.; Part II. Attempts to synthesize alkylphosphinyl imines from oximes using diphenylchlorophosphine and triethylamine at −50°C led instead to the corresponding phosphinyl enamides, which are apparently more thermodynamically stable. Attention was then turned to the utilization of the phosphinyl enamides in Diels-Alder cycloaddition reactions. This section describes the results. |
