115977-22-5Relevant academic research and scientific papers
syn-anti Isomerism in the 1,3-Dipolar Cycloaddition to cis-3,4-Disubstituted Cyclobutenes. Part 2. Role of Conformation in Bicyclohept-6-enes
Burdisso, Marina,Gandolfi, Remo,Pevarello, Paolo,Rastelli, Augusto
, p. 753 - 758 (1988)
Bicyclohept-6-ene (1a) and 2,4-dioxabicyclohept-6-ene (1b) reacted with diazomethane and phenylglyoxylonitrile oxide to give only anti adducts.In contrast, a mixture of syn and anti adducts was isolated from the reactions of the same 1,3-dipoles with bicyclohept-6-en-30one (1c), 2,4-dioxabicyclohept-6-en-3-one (1e), and even with the apparently most crowded, on the syn face, 3,3-dimethyl-2,4-dioxabicyclohept-6-ene (1d).Extensive ab initio MO calculations (4-31G) showed that compounds (1) prefer a boat-like conformation which, however, becomes flatter and flatter on passing from (1a) to (1e).As a result there is a progressive lessening of steric hindrance on the syn face which neatly parallels the observed increase in syn attack along the series (1a-e).Moreover the energy required to remove steric hinderance on passing from the boat-like to the half-planer conformation is definitively lower for (1c-e) than for (1b and a).
