Stereocontrolled reactions of iminosulfoxides

1 Stereoselective Reduction of (3-lminosulfoxides Application to the Synthesis of Nonracemic Amines 

While much effort has been concentrated on the stereoselective reduction of p-ketosulfoxides (Section 4.1), relatively little attention has been paid to the analogous reactions of P-iminosulfoxides or the corresponding enamine tautomers as an approach to chiral P-aminosulfoxides. 

The reduction of (23) is believed to proceed via imine tautomer (24) since enamines (25) are not reduced under identical reaction conditions. The high levels of diastereoselectivity were rationalized by postulation of a chelated transition state (27), which is similar in structure to those used to rationalize the diastereoselective reduction of p-ketosulfoxides described in Section 4.1. 

Examination of these results (Table 4.6) reveals that opposite diastereoselectivities are available by variation of the reducing agent. On employing L-selectride, diastereoisomer (31b) is preferred, while the ZnBr2/DIBAL reducing system selectively produces (31a). 

Transition states, similar in structure to those previously described above, have been proposed to explain the stereochemical outcome of these reductions. Transition state (32) shows the chelated intermediate giving rise to (31a). 

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