Opposite pi-face selectivity for the DMD and m-CPBA epoxidations of chiral 2,2-dimethyloxazolidine derivatives of tiglic amides: control by steric interactions versus hydrogen bonding
[formula: see text] A high extent but opposite sense in the diastereoselectivity has been observed for the DMD and m-CPBA epoxidations of the optically active tiglic amides (S)-1 with 2,2-dimethyloxazolidines as chiral auxiliaries. This unprecedented reversed pi-facial differentiation for these two peroxidic oxidants is rationalized in terms of like (lk) and unlike (ul) transition structures: For DMD, steric interactions dominate, such that the unlike transition structure is favored, while for m-CPBA, hydrogen-bonding effects overcome these steric repulsions and the like one is preferred.
Adam
W
Institut fur Organische Chemie, Universitat Wurzburg, Am Hubland, Germany. adam@chemie.uni-wuerzburg.de
Pastor
A
Peters
K
Peters
EM