The term bispericyclic reaction was famously coined by Caramella et al in 2002[1] to describe the unusual features of the apparently innocuous dimerisation of cyclopentadiene. It shows features of two paths for different pericyclic reactions, comprising a 2+4 cycloaddition in the early stages, but evolving into a (degenerate) pair of [3,3] sigmatropic reactions in the latter stages. Houk (who also uses the term ambimodal) has in recent years extended the number of examples of such pericyclic sequences to trispericyclic[2] (see here) and even an ambimodel tetrapericyclic reaction, as reported at the recent WATOC event. Here I show an example of a new type of bispericyclic reaction, comprising a 2+4 cycloaddition combined with a electrocyclic ring opening.
References
- P. Caramella, P. Quadrelli, and L. Toma, "An Unexpected Bispericyclic Transition Structure Leading to 4+2 and 2+4 Cycloadducts in the Endo Dimerization of Cyclopentadiene", Journal of the American Chemical Society, vol. 124, pp. 1130-1131, 2002. http://dx.doi.org/10.1021/ja016622h
- X. Xue, C.S. Jamieson, M. Garcia-Borràs, X. Dong, Z. Yang, and K.N. Houk, "Ambimodal Trispericyclic Transition State and Dynamic Control of Periselectivity", Journal of the American Chemical Society, vol. 141, pp. 1217-1221, 2019. http://dx.doi.org/10.1021/jacs.8b12674