Pseudorotational, conformational, and NOE studies of pentacovalent spirophospholenes derived from ephedrine and .alpha.-diketones

Abstract

Variable-temperature NMR studies showed the chiral pentacovalent dioxaphospholenes 1-3 to be pseudorotationally stable below 60 o C. ΔG PSDRRN for 1 and 2 were determined to be 22.0±2.1 kcal/mol and 33.0±2.6 kcal/mol, respectively. The ΔG PSDRTN for 2 is the largest value reported to date. 1 H NMR nuclear Overhauser effect studies on the major isomer of 1 confirmed that it was 1a and not 1b