 a novel oxidative 
 n - heterocyclic carbene - catalyzed reaction pathway 
 has been discovered . 
 alkyl and aryl enals undergo -hydroxylation 
 via oxygen atom transfer from electron - deficient nitrobenzenes , followed 
 by trapping of the resultant acyl azolium by the solvent . 
 the proposed 
 mechanism involves a single electron transfer event to initiate the 
 reaction followed by radical recombination . 
 this represents a profound 
 mechanistic departure from the established two - electron disconnects 
 in nhc catalysis . 
Supplementary Material