Enantioselective Alkylation of N-Arylhydrazones Derived from α-Keto Esters and Isatin Derivatives through Asymmetric Phase-Transfer Catalysis
The phase-transfer-catalyzed asymmetric alkylation reactions of N-arylhydrazones derived from α-keto-esters and isatin derivatives afford enantioenriched azo compounds that bear a tetra-substituted carbon stereocenter in good yields with high chemo- and enantioselectivity. The alkylation products can be readily converted into chiral amino esters, hydrazine derivatives, and aza-β-lactams without loss of enantiopurity.
Oxidation of hydrazones by hypervalent organoiodine reagents: Regeneration of the carbonyl group and facile syntheses of α-acetoxy and α-alkoxy azo compounds
Various hydrazone derivatives of α-keto esters were prepared. The carbonyl group was readily regenerated in high yield from phenylhydrazones through oxidative hydrolysis using hypervalent organoiodine(III) reagents either bis(trifluoroacetoxy)-iodobenzene (BTIB) in aqueous acetonitrile or hydroxy(tosyloxy)iodobenzene (HTIB) in chloroform. α-Acotxy phenyl- or methylazo compounds were readily synthesized by oxidation of the corresponding hydrazones with iodobenzene diacetate (IBDA) in dichloromethane or acetic acid. α-Methoxy phenyl- or methylazo compounds were also prepared by oxidation of the hydrazones in methanol. The mechanisms of the oxidation reactions are discussed.
Barton, Derek H. R.,Jaszberenyi, Joseph Cs.,Liu, Wansheng,Shinada, Tetsuro
p. 14673 - 14688
(2007/10/03)
Oxidation of phenylhydrazones of α-keto esters with hypervalent organoiodine reagents
α-Ketoacids and ketones can easily be regenerated in high yield from their phenylhydrazones via hydroxy azo compounds upon oxidation with hupervalent iodine reagents.
Barton, Derek H. R.,Jaszberenyi, Joseph Cs.,Shinada, Tetsuro
p. 7191 - 7194
(2007/10/02)
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