O esters

Diazomethane alkylation of A-4-thiazoline-2-ones (36, 214) or the Williamson reaction of 2-halogenothiazoles (6. 287-300) provide good yields of 2-alkoxythiazole otherwise obtained by reaction between O-esters of monothiocarbamic acid with a-halocarbonyl compounds (see Chapter II). 

The reason for this relative lack of reactivity of 2-methylthiazoIium is probably due to the too-weak nucleophilic character of its carbon-2. For example, any /S-alkoxyalcene (29) derivatives resulting from the condensation of o-ester could never have been isolated, whereas they constitute the essential intermediate step in trimethine syntheses for rings of acidic character (64). However, even if a negative 5-substituent such as ethoxy-carbonyl increases the yield (61) by promoting independently the possible formation of the methylene base, it may be stressed that the presence of this base is not the essential condition of the reaction, since the isolated anhydrobase itself is not reactive toward the o-ester (Scheme 41). 

The easier elimination of pyridine compared to quinoline-4 may be related to the pK value of 4-methylthiazole, which is between those of lepidine and 2-picoline (25. 55). This reaction explains also why a neutrodimethine cyanine is obtained with such good yields when reacting together a quaternary salt, ketomethylene, and o-ester in a basic medium. As the reaction proceeds, the trimethine cyanine is attacked by the ketomethylene. The resulting 2-methyl quaternary salt is transformed into trimethine cyanine, consuming the totality of the ketomethylene (1, p. 512 661). The mesosubstituted neutrodimethine cyanine is practically pure. 

Ring expansion of haloalkyloxiranes provides a simple two-step procedure for the preparation of azetidin-3-ols (Section 5.09.2.3.2(f)) which can be extended to include 3-substituted ethers and O-esters (79CRV331 p. 341). The availability of 3-hydroxyazetidines provides access to a variety of 3-substituted azetidines, including halogeno, amino and alkylthio derivatives, by further substitution reactions (Section 5.09.2.2.4). Photolysis of phenylacylamines has also found application in the formation of azetidin-3-ols (33). Not surprisingly, few 2-0-substituted azetidines are known. The 2-methoxyazetidine (57) has been produced by an internal displacement, where the internal amide ion is generated by nucleophilic addition to an imine. 

In the series NHR. CO. O. CgH. NMe all the members tried in which R is a methyl group were active, but when R is ethyl or hydrogen, miotic action is reduced or may even disappear, thus the p and m-dimethylaminophenyl esters of ethylcarbamic acid (R = C2H5) are inactive but the o-ester is active, indicating that activity is also influenced by the position and nature of the basic group. When the tertiary basic... 

J. Yield Icompari d ailh drv mati-rialj O O per coot., r/j-j 08741 an + 0 38 acid iiuiuhec l.j O ester number 2I5 4 ester nombcr after acetylation 28fj. 3 soluble in 0 8 and more volume 80 per cent, alcohol t.ot euUrely soluble in 70 per cent, alcohol. 

Monothiocarbonsaure-O-ester-amide werden analog den Carbamidsaure-estem (s. S. 128ff.) durch Lithiumalanat zu N-Methyl-aminen, Alkoholen und Schwefelwasserstoff reduziert ... 

Die Methode wird hauptsachlich zur Reduktion cyclischer Monothiocarbamidsaure-O-ester eingesetzt z. B.1 ... 

Im folgenden werden lediglich die Thiocarbonsaure-O-ester und -amide besprochen, da nur in diesem Fall eine echte C=S-Doppelbildung reduziert wird (zur Reduktion von Thiocarbonsauren bzw. deren -S-ester s. S. 265f.). 

Thiobenzoesaure-O-ester werden durch Tributyl-zinnhydrid zu Kohlenwasserstof-fen und Benzylthiol reduziert. Dieses ermoglicht die Oberfiihrung sek. Alkohole in Kohlenwasserstoffe1 z. B. ... 

The 1,3-disconnection can only be made at the di-rarbonyl oxidation level which means going all the way o ester (33) to preserve the distinction between the - vo groups. 

Compound (1) phosphorylates phosphate monoesters and alcohols, although with the latter a considerable excess of alcohol is necessary to obtain satisfactory yields. In the absence of mercuric ions the milder phosphorylating species (3) can be isolated which converts monoalkyl phosphates to pyrophosphate diesters in good yield but does not react appreciably with alcohols unless catalytic amounts of boron trifluoride are added. Amine salts of (3) are converted to phosphoramidates on heating. In the presence of silver ions, O-esters of thiophosphoric acid behave as phosphorylating agents and a very mild and convenient procedure suitable for preparing labile unsymmetrical pyrophosphate diesters, such as the... 

The equilibrium of the last step (3), which is not actually part of the condaisa-tion mechanism, is far to the right because of the greater basic strength of the ethoxide ion as compared to (IV), and this largely assists the forward reactions in (1) and (2). The reaction mixture contains the sodium derivative of the k o-ester, and the free ester is obtained upon acidification. 

Tris (dibuty Ibis (2-hydroxy ethylthio)stannane) O-ester with bis(boric acid) XK 4860000... 

Chemical names Phosphorothioic acid 0-[4-[(dimethylamino) sulfonyl], phenyl] 0,0-dimethyl ester Phosphorothioic acid, 0,0-dimethyl-, O-ester with p-hydroxy-/V,/V-dimethylbenzene sulfonamide Phosphorothioic acid, 0,0-dimethyl O-p-(dimethylsulfamoyl) phenyl ester O-Dimethyl hydrogen phosphorothioate, O-ester with p-hydroxy-/V,/V-dimethylbenzenesulfonamide 0-[4-1 (Dimethylamino) sulfonyl] phenyl phosphorothioic acid O.O-dimethyl ester O,O-Dimethyl O, p-(N,N-dimethylsulfamoyl) phenyl phosphorothioate O, p-(Dimethylsulfamoyl) phenyl O.O-dimethyl phosphorothioate p-(Dimethylsulfamoyl)phenyl dimethyl phosphorothioate O.O-dimethyl 0-[p-(dimethylsulfamoyl)-phenyl] phosphorothioate Dimethyl p-(dimethylsulfamoyl) phenyl phosphorothionate O.O-dimethyl-O, p-(dimethylsulfamoyl) phenyl phosphorothionate... 

Fundamentally, O-esters of N-hydroxy-2-thiopyridone are photo-lyzed in the presence of an excess of white phosphorus in a methylene chloride/carbon disulfide medium. On solvent removal, hydrolysis, and oxidation with hydrogen peroxide, good yields of phosphonic acids (Figure 2.10) bearing the carbon functionality of the parent acid are isolated. 

Figure 2.10 Preparation of phosphonic acids from O-esters of N-hydroxy-z-thiopyri-dones.

The UV spectra of nitronates, which are not functionalized at the a-C atom, have an intense absorption at 230 to 240 nm, which is very similar in characteristics to UV absorption of salts of nitro compounds and solutions of aci-nitro compounds in protic solvents. Since standard alkyl- or silyl nitronates cannot have ionic structures, the presence of the above mentioned absorption in the UV spectra of nitronates, unambiguously confirms, that these compounds have the structures of O-esters. 

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