Photoremovable chiral auxiliary^1


                Viju B. Kammath, Peter Šebej, Tomáš Slanina, Zdeněk Kříž, Petr Klán


Department of Chemistry, Faculty of Science, Masaryk University, Kamenice 5/A8, 625 00, Brno, Czech
                                             Republic



Chiral auxiliaries are optically active groups, temporarily covalently attached to the prochiral
substrate, that induce a selective formation of one of the enantiomeric products during a
stereoselective reaction. When the reaction stereochemistry is achieved, the auxiliary is removed.
The benzoin group has already been used as a photoremovable protecting group^2 for various
functionalities, such as carboxylates,^3 hydroxy compounds,^6 and phosphates.^4,5


Here we introduce a concept of photoremovable chiral auxiliary as a novel strategy in the field of
asymmetric organic synthesis, which offers an auxiliary that can be removed upon irradiation.
Enantiopure benzoin derivatives were utilized as such auxiliaries: A dienophile linked to this
group underwent a Diels-Alder reaction with a diene in the presence of various catalysts and the
auxiliary was removed photochemically. The released acids were obtained with very high enantiomeric
excess in some cases.



      1    Balachandran Kammath V., Šebej P., Slanina T., Køíž Z., Klán P.,
Phoremovable Chiral Auxiliary, Org. Lett. (submitted).

      2  Greene T.W., Puts P.G.M.: Protective groups in organic synthesis - 3rd ed., John Wiley
&    Sons, New York, USA, 1999

3     Sheehan, J. C.; Wilson, R. M. Journal of the American Chemical Society 1964, 86, 5277.

4     Givens, R. S.; Athey, P. S.; Kueper, L. W.; Matuszewski, B.; Xue, J. Y. Journal of the
American Chemical Society 1992, 114, 8708-8710.

5     Pirrung, M. C.; Shuey, S. W. Journal of Organic Chemistry 1994, 59, 3890-3897.

6     Pirrung, M. C.; Bradley, J. C. Journal of Organic Chemistry 1995, 60, 1116-1117.