Photochemical Rearrangement of <i>N</i>-Mesyloxylactams: Stereospecific Formation of <i>N</i>-Heterocycles

N-Mesyloxylactams undergo an efficient ring-contraction to N-heterocycles of various ring sizes. Yields increase with the degree of substitution α to the carbonyl. The stereochemical information of a chiral migrating carbon is conserved making this reaction a synthetically useful complement to the well-known Hofmann, Curtius, Lossen, and Schmidt rearrangements.