Oxidative selenofunctionalization of allenes: convenient access to 2-(phenylselanyl)-but-2-enals and 4-oxo-3-(phenylselanyl)pent-2-enoates

The controlled preparation of two types of alpha-seleno-alpha,beta-unsaturated carbonyls, namely, alpha-selenoenals and alpha-selenoenones, has been accomplished directly from allenes through metal-free oxidative selenofunctionalization reactions. The decisive role of organoselenium and 1-fluoropyridinium reagents has been disclosed. The divergent reactivity due to the presence or absence of an ethoxycarbonyl moiety at the allene end has also been studied. A tentative pathway implying selective electrophilic addition of the selenium reagent to the allene moiety followed by adventitious water attack and concomitant oxidation has been proposed.