Orthoesters structure

Selective reaction of the bromochloro compound 83 with silver fluoride in acetonitrile gave a good yield of the product of nucleophilic displacement of bromide with inversion of configuration, namely, 151, and treatment with an excess of the reagent afforded25 the g m-difluoride (152). With alcohols in the presence of silver triflate, compound 83 affords access to orthoesters (for example, the dimethyl compound 153), and with diols sp/ro-analogs (for example, 154, which has the orthoester structural feature of the orthosomy-cins), are obtained.88... 

Evans this behavior indicated the presence of acetylribosyl chloride. Since the isomeric n-arabinosyl-dihydroxyacetone tetraacetate of Kreider and Evans, which does not possess an orthoester structure, showed no reaction with hydrogen chloride in chloroform solution, it was concluded by Klingensmith and Evans that the behavior of the ribose derivatives is to be attributed to an orthoester structure. 

In 1935 Pacsu found that the replacement of the chlorine atom in acetylfructosyl chloride by a methoxyl group is not a simple exchange reaction. When acetylfructosyl chloride was treated according to Brauns with commercial silver carbonate in methanol for two hours at room temperature and then refluxed for fifteen minutes, a sirupy reaction product was obtained. For removal of a trace (2%) of fructose tetraacetate formed in the reaction as a by-product, a benzene solution of the sirup was extracted about twelve times with water until the aqueous extract did not reduce Fehling s solution. The sirupy residue from the dried benzene solution consisted of the dextrorotatory, crystalline methyl a-D-fructopyranoside tetraacetate (34%) of Schlubach and Schroter as well as 64% of a new isomer possessing the orthoester structure (IXa or b). A complete separation of the latter from the accompanying normal fructoside tetraacetate could not be accomplished. The best result was... 

Although Pacsu regarded these substances as (3)-monoacetyl-/3-methylfructoside 2,6) with orthoester structure and its triacetate (IXb), their true structure has not yet been rigidly determined. The alternate structures of 3,4,5-triacetyl-n-fructose methyl 1,2-orthoacetate (IXa) and D-fructose methyl 1,2-orthoacetate are still to be considered. 

Pacsu observed the formation of a new methyl (Xlla or b) and ethyl sorboside tetraacetate possessing the orthoester structure when acetylsorbosyl chloride was shaken either with absolute methyl or ethyl alcohol and silver carbonate for several hours at room temperature. The normal crystalline methyl and ethyl sorboside tetraacetates were obtained as by-products. The acetylsorbosyl chloride used in these experiments was prepared either according to the method of Schlubach... 

In conclusion, it can be stated that the lack of chemical reactions which are suitable for proving an acidic orthoester structure leaves the absorption measurements in the ultraviolet as the most promising method for the determination of structure. It would be veiy desirable if such measurements could be made on Ohle s monobenzoyl-derivative and on Pigman and Isbell s monobenzoyl-talose, since these molecules do not contain carbonyl groups in their orthoester forms. 

IR frequencies of functional groups, 206 polymer characterization procedure, 205 polymer synthetic procedure, 204 postpolymerization schedules, 204,205t properties, 206,207t study procedure, 205-206 Acrylate-containing spiro orthoesters, structures, 172,173/... 

Phosphate esters readily undergo intramolecular migration from one hydroxyl group to another under the influence of acid 171), (See Fig. 1, 172,) This migration probably proceeds through a cyclic compound similar to the orthoester structure proposed in acyl group migration (p. 147 and 433) ... 

An interesting reaction useful in testing for the orthoester structure is that which takes place with hydrogen chloride in chloroform. Under these conditions, the orthoester derivatives are converted to the normal 0-acetyl-glycosyl chlorides. 

The structure of the lactone was demonstrated by synthesis. Eliminating a three-atom ethylene oxide ring as improbable, the position of the alkali-resistant 0-acetyl group is located by this evidence as carbon 2. The resistance of this group to alkaline hydrolysis is indicative of an unusual structure. An orthoester structure agrees with this resistance as well as with the ease with which the acetyl and methyl groups are hydrolyzed by acids. The ordinary alkyl orthoacetates exhibit similar properties. 

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