Microwave-enhanced radical reactions at ambient temperature : Part 3: Highly selective radical synthesis of 3-cyclohexyl-1-phenyl-1-butanone in a microwave double cylindrical cooled reactor

The microwave-enhanced synthesis of 3-cyclohexyl-1-phenyl-1-butanone (CPB) from crotonophenone and iodocyclohexane in the presence of t-BuOOH and triethylborane was examined at ambient temperature and under reflux conditions in bulk solution using no less than four different synthetic protocols. Chemical yields of CPB (93 and 95%, respectively) obtained after 60 and 120 min under microwave dielectric heating coupled to a cooling system (MW/Cool protocol) for a reaction temperature of 20–24 °C exceeded the yields from the reaction occurring at room temperature (24 °C; no microwaves; 40% and 72%) for the same reaction times and temperature. The competitive radical reaction to produce CPB and a small amount of by-products generated from the thermally-induced synthesis by the non-selective radical reaction was restricted solely to the process occurring at ambient temperature (RT protocol), under microwave dielectric heating to reflux (MW protocol) and heating with an oil-bath also to reflux (Oil-bath protocol). By contrast, no by-products were generated or detected for the reaction taking place by the MW/Cool method. Comparison of product yields under conditions of identical temperature conditions must involve some specific microwave effect in the synthesis of the title compound.