| Abstract
| - Asymmetric oxidation of a range of 1,3-dithianes was studied using the Kagan protocol [CHP (4equiv), (+)-DET (2 equiv), Ti(OiPr)4 (1 equiv), and H2O (1 equiv) at −35 °C for 48 h]. 1,3-Dithianeitself gave monoxide (30% ee) and the trans bis-sulfoxide (59% ee) but with low enantioselectivity.In contrast, ester derivatives (Me, Et, t-Bu, Ph) of 1,3-dithiane-2-carboxylates gave monoxides (80−95% ee) and trans bis-sulfoxides (>97% ee) in high enantioselectivity. Optimum conditions for theoxidation of ethyl 1,3-dithiane-2-carboxylate required the Modena protocol [CHP (4 equiv), (+)-DET (2 equiv), and Ti(OiPr)4 (0.5 equiv) at −22 °C for 24 h], and this gave the trans bis-sulfoxidein 60% yield and high enantioselectivity. The bis-sulfoxides were found to be acid sensitive andrequired rapid workup and purification for optimum yields. The differences between the Modenaand Kagan oxidants are discussed together with a discussion on the origin of the high enantio-and diastereoselectivity of the reaction. Finally, hydrolysis and decarboxylation furnished trans-1,3-dithiane 1,3-dioxide.
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