Steric and Conformational Control of the Regioselectivities in the Ene Reaction with Trisubstituted Cycloalkenes:  Comparison of the Enophiles Singlet Oxygen, Triazolinedione, and Nitrosoarene

2000-09-19T00:00:00Z (GMT) by Waldemar Adam Nils Bottke Oliver Krebs
The nitrosoarene ene reaction with the cycloalkenes 13 and E-4 proceeds in high twix regioselectivity to afford the hydroxylamine ene products 1a4a (twix) and 1b4b (twin, except far E-4 twix). Steric interactions in the enophile attack are responsible for the skew trajectory of the nitrosoarene enophile. For Z-1-methylcyclooctene (Z-4), twin abstraction dominates, caused by conformational constraints (transannular interactions) in the hydrgogen-atom abstraction. The balance between these steric and conformational factors dictates the regioselectivity in the ene reaction