Chemoselective deacylation of functionalized esters catalyzed by dioxomolybdenum dichloride
摘要:
Among five different oxidometallic species and two Lewis acids investigated, MoO(2)Cl(2) shows the best catalytic and chemoselective activity for the deacylation of esters in methanol at ambient or elevated temperature. Both high efficiency and chemoselectivity were achieved for substrates bearing different ether or ester groups. Acylated mono and disaccharides can also be selectively deacetylated in good yields, leading to useful carbohydrate templates for further synthetic manipulations. (C) 2010 Elsevier Ltd. All rights reserved.
practical lanthanide(III)-catalyzed transesterification of carboxylic esters, weakly reactive carbonates, and much less-reactive ethyl silicate with primary and secondary alcohols was developed. Heterobimetallic dinuclear lanthanidealkoxide complexes [Ln2Na8(OCH2CH2NMe2)}12(OH)2] (Ln = Nd (I), Sm (II), and Yb (III)) were used as highly active catalysts for this reaction. The mild reaction conditions enabled
The first Lewis acid catalyzed protection of alcohols as Boc derivatives is described. Zinc acetate is a very efficient catalyst for this transformation and the reaction can be applied to primary, secondary and aromatic alcohols, providing the first example of a generally applicable method.
Nucleophilic Acyl Substitutions of Anhydrides with Protic Nucleophiles Catalyzed by Amphoteric, Oxomolybdenum Species
作者:Chien-Tien Chen、Jen-Huang Kuo、Vijay D. Pawar、Yogesh S. Munot、Shieu-Shien Weng、Cheng-Hsiu Ku、Cheng-Yuan Liu
DOI:10.1021/jo048363v
日期:2005.2.1
[GRAPHICS]Among six different group VIb oxometallic species examined, dioxomolybdenum dichloride and oxomolybdenum tetrachloride were the most efficient catalysts to facilitate nucleophilic acyl substitution (NAS) of anhydrides with a myriad array of alcohols, amines, and thiols in high yields and high chemoselectivity. In contrast to the well-recognized redox chemical behaviors associated with oxomolybdenum(VI) species, the catalytic NAS was unprecedented and tolerates virtually all kinds of functional groups. By using benzoic anhydride as a mediator for in situ generation of an incipient mixed anhydride -MoO2Cl2 adduct with a given functional alkanoic acid, one can achieve oleate, dipeptide, diphenylmethyl, N-Fmoc-alpha-amino, pyruvic, and tert-butylthio ester, N-tert-butylamide, and trityl methacrylate syntheses with appropriate protic nucleophiles. The amphoteric character of the Mo=O unit in oxomolybdenum chlorides was found to be responsible for the catalytic NAS profile as supported by a control NAS reaction of using an authentic adduct-MoOCl2(O-2-CBut)(2) between pivalic anhydride and MoO2Cl2 as the catalyst.
Catalytic Nucleophilic Acyl Substitution of Anhydrides by Amphoteric Vanadyl Triflate
[GRAPHICS]Among four vanadyl species examined, vanadyl triflate was the most efficient catalyst to facilitate nucleophilic acyl substitution of anhydrides with a myriad array of alcohols, amines, and thiols in high yields and high chemoselectivity. By using mixed-anhydride technique, one can achieve oleate and peptide syntheses. In marked contrast to common metal triflates, the amphoteric character of the V=O unit in vanadyl species was proven to be responsible for the catalytic profile in this process.
Houlihan, F.; Bouchard, J.; Frechet, J. M. J., Canadian Journal of Chemistry, 1985, vol. 63, p. 153 - 162
作者:Houlihan, F.、Bouchard, J.、Frechet, J. M. J.、Willson, C. G.