Generation of Stereocenters Around a C3-Symmetric Cyclotriveratrylene Crown

Abstract

The oxidation of racemic methylthio-substituted C3-symmetric cyclotriveratrylene (CTV) 2 produces the corresponding trisulfoxides 3 as follows. Oxidation with m-chloroperoxybenzoic acid (m-CPBA) in dichloromethane leads to the formation of a distribution of the four possible diastereomers that is relatively close to the statistical outcome, in which the C3-symmetric stereoisomers are the minor species. In contrast, the optically active Davis reagent [oxaziridine (+)-4] in carbon tetrachloride at room temperature leads to a biased (73 %) distribution in favor of the C3-symmetric MRRR/PSSS diastereomer of 3 with 56 % ee (PSSS enantiomer according to the model of Davis). Interestingly, when the oxidation is carried out in toluene at reflux, the distribution is switched to approximately equal amounts of the C3-symmetric MSSS/PRRR and asymmetric MRSS/PSRR diastereomers of 3. Overall, however, these results point to the negligible role played by the chirality of the CTV platform on the induction of chirality at the sulfur prochiral centers.