Benzoates acyl migration

Acyl migration is a reversible process, and external factors (for example, solubility) can influence the equilibrium. Thus, after dissolution of methyl 2-0-benzoyl-4,6-0-benzylidene-a-D-glucopyranoside in acetone-aqueous sodium hydroxide, almost immediate crystallization of the 3-benzoate occurred, in 65% yield.549 Similarly, benzyl 3-0-benzoyl-4,6-0-benzylidene-/3-D-galactopyranoside yielded the 2-... 

The scope of the AD was further broadened by the discovery that ally] 4-methoxy-benzoates are excellent substrates for this reaction [8]. The 4-methoxybenzoyl substituent is supposed to interact with the aryl groups of the ligand-binding pocket and to suppress acyl migration from... 

The Fries reaction can also be metal-promoted to afford, under the proper reaction conditions, good yields of specific ortho acyl migration products. For instance, o-bromophenyl pivaloate (248) has been treated at —95 °C with s-butyllithium to afford o-hydroxypivalophenone (249) in 76% yield (equation 178) . Similarly, benzoate 250 gave o-hydroxyketone 251 in 82% yield by treatment with n-butyllithium (equation 179) °. 

Aryl benzoates are subject to acyl migration under basic conditions. ... 

Studies of Trifluoroacetic Acid. Part VII, The Synthesis of 2-BenzoyI-4 6-Benzyli-dene Methyl-a-D-glucopyranoside and its Conversion into the Isomeric 3-Benzoate by an Acyl Migration, E. J. Bourne, A. J. Huggard, and J. C. Tatlow,/. Chem. Soc., 735-741 (1953). 

Reaction of hypobromous or hypochlorous acids with cholest-4-en-3j8-ol acetate or benzoate (160) gives the 5a-halogeno-3) ,4 -diol 4-monoester, (162) via the acyloxonium ion (161). The 3-monoesters (163) are available by opening of the 4/ ,5)9-epoxide (164). The facility of acyl migration between the two oxygen substituents is revealed by the formation of the 4) ,19-ether (165) when either monoester (162) or (163) was treated with lead tetra-acetate cf. p. 386). ... 

In summary, it may be stated that the reaction of acyl esters of aldoses and aldobioses (see Section III, p. 92) with ammonia consists of a set of competitive pathways, including intramolecular O —> N migrations of acyl groups, deacylations, and transesterifications, with formation of aldose amides and variable proportions of the free sugar as the principal products. Significant proportions of basic or insoluble polymeric substances were not observed with aldose acetates or benzoates, although occurrence of extensive browning indicates the probable formation of soluble melanoidins. 

Table VI gives the exciton migration lengths for five copolymers of ACN obtained by reacting poly(ACN-co-vinyl alcohol) with different acyl chlorides. The migration length as a percentage of the end-to-end distance is 167% for poly(ACN-co-l-vinyl naphthoate). For fluorophores 2-vinyl naphthoate, vinyl benzoate and vinyl cinnamate the average is 116% and for dimethyl-(2-naphthoxy)vinyloxysilane, 146%.

---