Sequential norrish type ii photoelimination and intramolecular aldol cyclization of 1,2-diketones in carbohydrate systems: stereoselective synthesis of cyclopentitols

Opened and closed: Visible-light photostimulation of 2,3-diuloses I triggers an unprecedented sequential rearrangement: A Norrish type II photoelimination to give an isolable acyclic photoenol intermediate II is followed by an intramolecular enolexo aldolization. The contraction of the pyranose ring in this process leads to a new type of cyclopentitol derivative III. R=acyl, alkyl, silyl group.