Theoretical and Experimental Studies on the Thermal Ring-Opening Reaction of Cyclobutene Having a Stannyl Substituent at the 3-Position
journal contributionposted on 23.01.2004, 00:00 by Masahiro Murakami, Munehiro Hasegawa, Hideyuki Igawa
The ring-opening reaction of 3-(trimethylstannyl)cyclobutene gave a mixture of the (Z)- and (E)-1,3-dienes, whereas that of 3-tert-butylcyclobutene exclusively afforded the (E)-1,3-diene due to the steric influences. The contrasting rotational behaviors suggest that there is some effect operating with the 3-stannylcyclobutene to stabilize the inward transition state, counteracting the steric influences. This contrasteric effect is ascribed to negative hyperconjugation. The stannyl group in the inward transition state accommodates electron density from the breaking σ orbital of the cyclobutene into its low-lying tin−carbon σ* orbital. Theoretical studies supported this interpretation.