Further investigations on the chemistry and structure of angustifoline and its derivatives. Part 6. New evidence of factors responsible for basicity of α-cyanoamines: crystal and molecular structure of N-cyanomethylangustifoline

Abstract

The crystal and molecular structure of N-cyanomethylangustifoline (III) has been determined from three-dimensional X-ray data by direct methods and refined by full-matrix least-squares calculations to a final R of 0.039 for 1 055 observed reflections. Crystals are monoclinic, a= 10.223(1), b= 9.416(1), c= 7.846 4(7)Å, β= 94.741(8)°, space group P2₁, and Z= 2.

The conformation of the cyanomethyl group was found to be the same as that preferred in solution. The lone pair at nitrogen N(12), bearing the cyanomethyl group, is trans to the nitrile group and gauche to the methylene hydrogen atoms. Possible factors stabilizing this conformation are discussed. Direct electrostatic interactions through space between the lone pair and ‘acidic’ protons of the bridging methylene group may cause a greater decrease in the basicity of α-cyanoamines than that due to the inductive effect of the nitrile group.

There is a weak C–H ⋯ OC intermolecular hydrogen bond [3.284(5)Å].