Vedejs reagent

Stereoselective a-hydroxylation of p-trifluoromethyl esters Hydroxylation of the ester 1 with the Vedejs reagent results in predominate formation of the (2S,3S)-isomer. NaBH4 reduction of the ketone 3 shows opposite stereoselectivity. Since the steric bulk of CF3 is similar to that of CH3, electronic factors may be important. 

Enolate hydroxylation cf. 11, 108).- Enolates of ketones or esters are oxidized by this oxaziridine to a-hydroxy carbonyl compounds. Yields are highly dependent on the base they are highest with potassium hexamcihyldisilazide. Yields are generally higher than those obtained with the Vedejs reagent (MoOPH, 8, 207). 

In a comparative study the authors demonstrated that aminium salt oxidation nicely complements the regioselectivity of other a-hydroxylation methods [173-180], which do not occur via electron transfer. Thus, using the Vedejs reagent [178] two positional isomeric products 83 and 84 were obtained from 82, whereas aminium salt oxidation leads to only one product. 

Reaction of enal 118, obtained by formylmethylene triphenylphosphorane treatment of 2,3-0-isopropylidene-D-glyceraldehyde with the Vedejs reagent 119... 

Due to its steric demand, LDA even leads to the less substituted enolate 18a from 2-phenylcyclohexanone, and the formation of the thermodynamically favored conjugated regioisomer is widely suppressed, as proven by oxidation with Vedejs reagent MoOj pyridine hexamethylphosphoric triamide (HMPA) leading diastereoselectively to hydroxyketone 19 [30]. To give a more recent example, the... 

Recently, Smulik and Vedejs have reported that sodium and potassium salts of phenylacetates, phenylacetonitriles, malonates and / -cyanoesters can be converted to their a-amino derivatives in good yields using 4a and 4b as amination reagents (Scheme 45) . Amination can be accomplished at lower temperature using 4b. 

E. Vedejs, Encyclopedia of Reagents for Organic Synthesis, John Wiley and Sons, Inc., L. A. 

Tin hydride reagents have been commonly used in radical-chain reductions in synthetic organic chemistry. It was reported by Vedejs and coworkers134 that the amino tin hydride reagent [o-(dimethylaminomethyl)phenyl]dimethyltin hydride (48) did not reduce esters,... 

VAN LEUSEN Reagent 397 VEDEJS Hydroxylation 398 Venketaraman 14 Verisy 251 VHIiger 13 Vnhe 399... 

Application of the Wittig reaction of a nonstabilized ylide to the synthesis of an ( )-alkene is practically and effectively carried out by the Schlosser modification. Alternatively, the use of a trialkylphos-phonium ylide can produce high ratios of ( )-alkene." Recently, Vedejs has developed a reagent using dibenzophosphole ylides (110) to synthesize ( )-disubstituted alkenes (111) fixnn rddehydes (equation 24). The initial addition of ylide occurs at -78 C, but the intermediate oxaphosphetane must be heated to induce alkene formation. The stereoselectivity in the process is excellent, particularly for aldehydes with branched substitution a to the reacting center. Both the ethyl and butyl yli s have b n utilized. 

With a parallel kinetic resolution, the two reactions should not interfere with one another. In the example above, both reactions were acylations but the use of stoichiometric reagents meant that the right acylating group was attached to the right enantiomer. Even here, Vedejs does not rule out a small amount of leakage between the paths (once the chiral DMAP is liberated it can get in on the act with the other pathway). A PKR becomes more difficult if, in addition to the reactions being related, they are also catalytic. 

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