تسجيل الدخول

تسجيل

Predominantly E alkenes can be formed by stereoselective elimination reactions

المؤلف:  Jonathan Clayden , Nick Greeves , Stuart Warren

المصدر:  ORGANIC CHEMISTRY

الجزء والصفحة:  ص684

2025-07-05

712

saw that E1 elimination reactions usually give mainly E alkenes because the transition state leading to an E double bond is lower in energy than that leading to a Z double bond. In other words, E1 reactions are stereo selective, and their stereoselectivity is kinetically controlled. E2 reactions are similar if there is a choice of protons that can be removed: the E alkene is preferred, but a mixture is still formed. Again, this is kinetic control.

Both stereo- and regioselectivity are usually better in E1cB reactions, such as the opening of this unsaturated lactone in base. The double bond inside the ring remains Z but the new one, formed as the ring opens, prefers the E geometry. The transition state for the elimination step already looks like the product and prefers the E geometry for simple steric reasons.