Ortho esters compounds

TABLE 5 Comparing the Shaping of a Poly(ortho ester) Compound by Flux-Mixing with 5 wt% Stearic Acid... 

Some early work on copolymer-compatibilized PPE-PPS blends is summarized in Arashiro et al. (1992). PPE-PPS blends have also been compatibilized through copolymer formation between citric acid-functionalized PPE (e.g., 162 parts) and PPS (e.g., 225-275 parts) in the presence of a multifunctional epoxy resin (0-17.5 parts) and a minor amount of PBT (25-50 parts) (Brown et al. 1997a) or in the presence of a epoxy-functionalized PO and a catalyst (Brown et al. 2001) or in the presence of a bifunctional cyclic ortho ester compound (Brown et al. 1998a). See also Dekkers (1989) and Inoue et al. (1990). Okabe et al. (1989) have prepared compatibilized blends comprising PPE-g-MA and amine-functionalized PPS in the presence of 4,4 -diphenylmethane diisocyanate coupling agent. 

The allylic geminal diacetate 141 undergoes the monoallylation of malonates to give 142 and the two regioisomers 143 and 144[93,94]. The dimethylacetal 145 or ortho esters of aromatic and a,/3-unsaturated carbonyl compounds react with trimethylsilyl cyanide to give the methyl ether of cyanohydrin[95]. 

The 1,3-dicarbonyl components can be replaced by an enol ether, which can be prepared by Claisen condensation from an ortho ester and a reactive methylene compound. ... 

The final stages of the successful drive towards amphotericin B (1) are presented in Scheme 19. Thus, compound 9 is obtained stereoselectively by sodium borohydride reduction of heptaenone 6a as previously described. The formation of the desired glycosida-tion product 81 could be achieved in dilute hexane solution in the presence of a catalytic amount PPTS. The by-product ortho ester 85 was also obtained in approximately an equimolar amount. Deacetylation of 81 at C-2, followed sequentially by oxidation and reduction leads, stereoselectively, to the desired hydroxy compound 83 via ketone 82. The configuration of each of the two hydroxylbearing stereocenters generated by reduction of carbonyls as shown in Scheme 19 (6—>9 and 82->83) were confirmed by conversion of 83 to amphotericin B derivative 5 and comparison with an... 

Note 1. The last two examples contain cyclic ortho ester structures. These compounds are conveniently named as cyclic acetals. 

The alkoxyl group OR is not a leaving group, so these compounds must be converted to the conjugate acids before they can be hydrolyzed. Although 100% sulfuric acid and other concentrated strong acids readily cleave simple ethers, the only acids used preparatively for this purpose are HBr and HI (10-71). However, acetals, ketals, and ortho esters are easily cleaved by dilute acids. These compounds are... 

TABLE Comparing the Compounding of Poly(ortho ester) with 5 wt% Stearic Acid Using Different Compounding Methods... 

This ring system is represented by tricyclic ring system 533 (76JHC1249). Reaction of 3-hydrazino[l,2,4]triazin-5-ones 531 with 3-imi-nobutyronitrile afforded 6-methyl- (or phenyl-) 3-[3-methyl-5-aminopyra-zolyl]-2,5-dihydro[l,2,4]triazin-5-ones 532A, which may exist in tautomeric form 532B. Its reaction with diethoxymethyl acetate (DEMA) or ortho-esters afforded the tricyclic compounds 533. 

Cyclization of 776 with ortho-esters gave (83JOC1628) [l,2,4]triazolo-[4,3-fc]pyrimido[5,4-< ][ 1,2,4]triazines 777, whereas reaction with sodium nitrite afforded the corresponding tetrazolopyrimidotriazine 778.3-Azido-pyrimido[4,5-e][l, 2,4]triazine 779 exists in a cyclic form as tetrazolo derivative 780, as shown by X-ray analysis (86KGS114). In solution the position of the 779 780 equilibrium depended on temperature and solvent. Higher temperatures favored 779. Azido compound 779 predominated in water, and tetrazolo compound 780 predominated in pyridine. Addition of sodium azide to the aqueous solution shifted the equilibrium toward 780. The... 

Imidates are a different type of imine. Conceptually, imidates result from dehydration after condensation of a primary amido N-atom with the carbonyl of an ester function, although the actual synthetic route is often via an ortho ester (RC(OR )3). A large variety of A-sulfonyl imidates have been prepared and examined for their value as potential prodrugs containing a sulfonamide or an ester moiety [101][102], The hydrolysis of such compounds,... 

The third spectrum is that of the compound trihydroxytitanium stearate the fourth, of triisopropoxytitanium stearate. The small differences between these spectra and those of the ortho esters are in the splitting of the principal peak. 

In addition to the activation of carbonyl compounds and imines, Schreiner studied on thiourea-catalyzed acetalization reaction, in which ortho esters were activated by hydrogen bond [19]. Jacobsen has utilized the hydrogen-bond catalysis in reactions with acyliminium ions, wherein hydrogen bond activates the acylim-inium salt through complexation with chloride [20]. 

Some organosilieon compounds undergo transmetallation. The allylic cyanide 461 was prepared by the reaction of an allylic carbonate with trimethylsi-lyl cyanide[298]. The ortho esters and acetals of the a. uJ-unsaturated carbonyl compounds 462 undergo cyanation with trimethylsilyl cyanide[95]. 

Addition of ketene acetals to a,j8-unsaturated carbonyl compounds to give ortho esters [18, 144]. 

Alcoholysis of trihalides 0-6 Hydrolysis of ortho esters 0-20 Alcoholysis of acyl halides 0-21 Alcoholysis of anhydrides 0-22 Esterification of carboxylic acids 0-23 Transesterification 0-24 Alkylation of carboxylic acid salts 0-25 Cleavage of ethers with anhydrides 0-26 Alkylation of carboxylic acids with diazo compounds... 

Enol Ethers and Esters 0-15 O-Alkylation of carbonyl compounds with diazo alkanes 0-17 Transetherification 0-20 Reaction between acyl halides and active hydrogen compounds 0-23 Transesterification 0-24 Acylation of vinylic halides 0-94 Alkylation with ortho esters 0-107 O-Acylation of 1,3-dicarbonyl compounds... 

Substituent effects on the A,u I reaction have been studied by Bender and Chen55. These authors measured the rates of hydrolysis of a series of 4-substituted 2,6-dimethylbenzoates in 9.70 M sulphuric acid at 25°C, and found that the values for the first-order coefficients with 4-methoxy, 4-methyl, 4-unsubstituted and 4-bromo-compounds (5.0, 0.37, 0.033 and 0.01 x I0 4 sec-1, respectively) are satisfactorily correlated by the Hammett equation, following cr+ with a slope p = —3.22. Since the esters are not fully protonated in 9.70 M H2SOj, part of this factor is due to the effects of the 4-substituent on the protonation equilibrium, p for the protonation of substituted benzoic acids is about — l35, but is likely to be considerably smaller for di-ortho-substituted compounds, since the conjugative interaction of the p-substituents with the protonated carboxyl group requires coplanarity with the ring. 

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