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.