Theoretical and experimental studies on the thermal ring-opening reaction of cyclobutene having a stannyl substituent at the 3-position.
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 sigma orbital of the cyclobutene into its low-lying tin-carbon sigma orbital. Theoretical studies supported this interpretation.
Murakami
Masahiro
M
Department of Synthetic Chemistry and Biological Chemistry, Kyoto University, Katsura, Kyoto 615-8510, Japan. murakami@sbchem.kyoto-u.ac.jp
Hasegawa
Munehiro
M
Igawa
Hideyuki
H