Variable Markovnikov orientation and cis effect in ene reactions of nitrosocarbonyl intermediates

Nitrosocarbonyl intermediates, generated at room temperature by the mild oxidation of nitrile oxides, undergo clean ene reactions with trisubstituted olefins. Allylic hydrogens on the more congested side of the alkene are exclusively abstracted (the “cis effect”), thus resembling singlet oxygen behavior. Nitrosocarbonyl benzene follows a Markovnikov orientation and abstracts preferentially the twix hydrogens over the lone ones. With the more sterically demanding nitrosocarbonyl mesitylene, the Markovnikov directing effect is relieved, and comparable twix and lone abstraction are observed.