On the Origin of Cis Selectivity in the Cyclization of N-Protected 2-Substituted 3-Aza-5-hexenyl Radicals: A Density Functional Study
作者:David Shanks、Stefan Berlin、Magnus Beşev、Henrik Ottosson、Lars Engman
DOI:10.1021/jo030294h
日期:2004.3.1
Cyclization of the N-dimethylphosphinoyl-2-methyl-3-aza-5-hexenyl radical has been studied at the UB3LYP/6-31+G(d)//UB3LYP/6-31G(d) hybrid density functional level. The corresponding radical precursor has been synthesized and found to give cis/trans ratios of up to 10/1 in reductive radical cyclizations. The relative energies of reactant and transition state conformers were determined. In discord with the Beckwith-Houk model, it has been found that chair-axial transition states, which lead to cis products, are lowest in energy, rationalizing the observed experimental diastereoselectivity.