Orthoesters and Related Derivatives

Carbonates and Related Derivatives Other Carboxylate Esters Esters ofNon-Carboxylic Acids OF GLYCOL SYSTEMS Cyclic Acetak, Ketak, and Orthoesters... 

Pinto and co-workers [75] have chosen a more traditional approach toward establishing 1,2-thio linkages and ultimately the production of thiokojibiosides and related derivatives. The thiol 187 was coupled to the P-trichloroacetimidate 188 thereby yielding the protected allyl kojibioside 189 [75] (Scheme 37). Interestingly, when the a-trichloroacetimidate 190 was used as donor the thiosophorose derivative 191 was obtained as the major product (191 192, 2.3 1) in a reaction proceeding via the stable orthoester 193. 

Couquelet and co-workers described the cyclization of the tetrahydrothiazolyl acid hydrazine 370 <1998BMC349> when this compound was refluxed in DMF in the presence of an orthoester, cyclization to 371 took place. The yield in certain cases was very low, in some other cases poor to medium (9-54%). A different synthetic strategy to a related derivative of the same ring system was published by Obreza and Urleb <2003SC1011>. These authors treated the N-substituted tetrahydrothiazole derivative 372 with hydrochloric acid in acetic acid solution. Cyclization to 373 took place in excellent yields (84-93%). 

From orthoesters, orthoamide derivatives and related compounds... 

Use of dibutyltin dimethoxide in place of dibutyltin oxide has been recommended for procedural simplicity and improved reproducibility in legioselective acylations, fcM example at 03 of diol 13. Moderate selectivity has been observed in the benzylation of thioglucoside derivative 14 and related compounds with benzyl bromide under phase transfer conditions. Opening of the known 2,3-carbonate 15 with ethanol or dodecanol gave the two expected 2- and 3-monoesters in nearly equal proportions.A new method for the selective diprotection of a-D-mannopyranosides involved opening of diorthoesters 16 which were formed in situ, as shown in Scheme 1. As only the 2,3-orthoesters opened regioselectively, the 2,4- and 2,6-dibenzoates 17 and 18, respectively. 

Regioselective debenzoylation of nucleoside 2, 3 5-tri-O-benzoates using hydrazine hydrate has been reported. With 1 mol reagent in acetic acid-pyridine the 3 5-di-O-benzoyl derivative was produced when the bases were adenine, guanine, or indole, whereas with excess hydrazine hydrate in 1 1 chloroform-methanol, 98% of the 5-O-benzoyl derivative was produced (base = adenine or uracil). 3, 5-Di-O-benzoyl-2-deoxy-nucleosides gave a 90% yield of a 1 1 mixture of 3 - and 5-O-benzoyl nucleosides with 1 mol hydrazine hydrate in pyridine. Treatment of the mannose orthoacetate (5) with benzoyl chloride in pyridine gave 2,3,4,6-tetra-O-acetyl-a-D-mannopyranosyl chloride and ethylbenzoate, whereas the related orthoester of mu co-inositol (6) gave 66% of the correspond-... 

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