Influence of cyclodextrin encapsulation on Norrish-Yang photoreaction of valerophenone

In the solid-state Norrish-Yang photoreaction of valerophenone, studied in presence of various cyclodextrins, not only was elimination suppressed, but a remarkable diastereoselectivity was also observed. The predominant formation of one cyclobutanol (C-1-trans) is rationalized as being due to a restricted rotational motion of the 1,4-biradical, and also stabilization of the same by hydroxyl groups present in the rim of the cyclodextrin cavity. Additional supports for the coinclusion of a side chain into the gamma-CD cavity from molecular minimization calculations and H-1-H-1 NOESY spectra are also presented.