Journal of the American Chemical Society p. 1428 - 1437 (1992)
Update date:2022-07-29
Topics:
Davis, Franklin A.
Thimma Reddy
Han, Wei
Carroll, Patrick J.
The synthesis, structure, and enantioselective oxidations of a new chiral N-sulfonyloxaziridine 12c [3,3-dichloro-1,7,7-trimethyl-2'-(phenylsulfonyl)spiro[bicyclo[2.2.1]heptane-2, 3'-oxaziridine]] are reported. This oxidant, which exhibits remarkably high and predictable ee's for the enantioselective oxidation of prochiral sulfides to sulfoxides, is prepared in three steps from (+)- or (-)-camphor in 50% overall yield. Steric effects are primarily responsible for the molecular recognition and are predictable using a simple active-site model where the nonbonded interactions between the RL and RS groups of the sulfide (RL-S-RS) and the active-site surface are minimized in a planar transition-state structure. The fact that alkyl aryl sulfides give high ee's in nonpolar solvents suggests that there is also a stereoelectronic component to the molecular recognition. High ee's (>90%) are anticipated for those sulfides where the difference in size of the groups directly bonded to the sulfur atom is large, i.e., aryl, tert-butyl vs CH2R (R = H, alkyl, benzyl, etc). The X-ray structure and studies with the dihydro, difluoro, and dibromo oxaziridines 12a, 12b, and 12d reveal that the exceptional enantioselectivities displayed by 12c are a consequence of a molecular cleft or groove, defined by the oxaziridine chlorine atoms and phenylsulfonyl group, on the active-site surface.
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