An electrocyclic reaction potentially can give two stereoisomeric products, one via an orbital symmetry allowed route and a second via either a forbidden route or a symmetry- independent route. The allowed route is well established, and the AAH* between it and the other routes has been estimated for the cyclobutene-butadiene2 and
![Benzene, [(1Z)-2-bromoethenyl]- Structure](https://image.chemsrc.com/caspic/491/588-73-8.png)
