Catalytic Allylic Amination versus Allylic Oxidation: A Mechanistic Dichotomy

Abstract

Allylic oxidation of hydrocarbon substrates is the foundation of many industrial and fine-chemical production processes. Direct allylic oxidation of cycloalkenes (C5-8) has been widely discussed in the chemical literature. However, certain mechanistic details related to the presence of allylic free radicals have yet to be fully resolved. The corresponding copper-catalyzed allylic amination reaction has not been previously achieved. We report the first examples of this class of amination reaction using saccharin and bis-p-toluenesulfonamide as nitrogen sources and t-BuOOH and PhI(saccharinate)2 as oxidants. Kinetic studies on stoichiometric model reactions demonstrate that the oxidant is not involved in the RDS of the transformation, and studies with 3,3,6,6-tetradeuteriocyclohexene conclusively show a mechanistic dichotomy between the catalytic oxidation and amination reactions. Both oxidative processes involve η1-allyl intermediates, and regiochemical results are a consequence of discrete copper complexes. A mechanistic rationale involving allylic transpositions explains this mechanism dichotomy.