Steric and conformational control of the regioselectivities in the ene reaction with trisubstituted cycloalkenes: comparison of the enophiles singlet oxygen, triazolinedione, and nitrosoarene
The nitrosoarene ene reaction with the cycloalkenes 1-3 and E-4 proceeds in high twix regioselectivity to afford the hydroxylamine ene products 1a-4a (twix) and 1b-4b (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
Intermediates in the ene reactions of singlet oxygen and N-phenyl-1,2,4-triazoline-3,5-dione with olefins
The reaction between singlet oxygen and cis- and trans-2-butene-1,1,1-d 3 has been studied. The product isotope effects (k H /k D ) were found to be 1.38 and 1.25, respectively. Similarly, N-phenyl-1,2,4-triazoline-3,5-dione (PTAD) reacts readily with these substrates and shows isotope effects that are larger (5.36, 1.29) but in the same direction. 2-Methyl-1-propene-3,3,3-d 3 is unreactive with singlet oxygen but reacts easily with PTAD with a product isotope effects of 1.25
Mechanism of palladium(II)-copper(II)-mediated demercuration of cycloalkyl and cycloalkylmethyl systems
The palladium(II)-copper(II)-mediated demercuration of cycloalkyl- and cycloalkylmethylmercuric chlorides exhibit mechanistic changes as a function of ring size, with elimination-readdition of [HPdX] being important in cyclohexyl systems but direct carbocation formation dominating in cyclooctyl cases.