Vedejs

Accumulating evidence makes it increasingly clear that there is no single dominant Wittig transition state geometry and, therefore, no simple scheme to explain cis/trans selec-tivities. The conventional betaine pathway may not occur at all, the stabilized ylides, e,g., PhsP—CH —C02Et, can be ( )- or (Z)-selective, depending on the solvent and substrate (E. Vedejs, 1988 A, B, 1990). 

E. Vedejs (1978) developed a general method for the sterically controlled electrophilic or-hydroxylation of enolates. This uses a bulky molybdenum(VI) peroxide complex, MoO(02)2(HMPTA)(Py), which is rather stable and can be stored below 0 °C. If this peroxide is added to the enolate in THF solution (base e.g. LDA) at low temperatures, oneO—O bond is broken, and a molybdyl ester is formed. Excess peroxide is quenched with sodium sulfite after the reaction has occurred, and the molybdyl ester is cleaved to give the a-hydroxy car-... 

Stibinitted by Jiro Tsuji, Hideo Nagashima, and Hisao Nemoto -. Checked by Edwin Vedejs, J. Gegner, and T. K. Mailman. 

For some important mechanistic studies and insightful discussions, see (a) Vedejs, E. Snoble, K.A.J. 

Vedejs et al. demonstrated that lithium-tin exchange is a feasible route to nonstabilized lithiated aziridines. Treatment of stannylaziridine 258 with n-BuLi gave lithiated aziridine 259, which could be trapped with a variety of electrophiles such as benzaldehyde (Scheme 5.66) [92]. Furthermore, simple N-alkyl aziridine 261 can be activated by Fewis acid precomplexation to BH3 (to give 262) and subsequently... 

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