Ammonium acetate carboxylic acid esters

To a solution of 5-methoxymethoxy-7-oxa-bicyclo[4.1.0]hept-3-ene-3-carboxylic acid methyl ester (4.9 g, 22.9 mmol) in 8/l-Me0H/H20 (175 ml, v/v) was added sodium azide (7.44 g, 114.5 mmol) and ammonium chloride (2.69 g, 50.4 mmol) and the mixture was refluxed for 15 h. The reaction was diluted with water (75 ml) to dissolve precipitated salts and the solution was concentrated to remove methanol. The resulting aqueous phase containing a precipitated oily residue was diluted to a volume of 200 ml with water and was extracted with ethyl acetate (3 times 100 ml). The combined organic extracts were washed with saturated NaCI (100 ml), dried (MgS04), filtered and evaporated. The crude was purified on silica gel (1/1-hexane/ethyl acetate) to afford 5-azido-4-hydroxy-3-methoxymethoxy-cyclohex-l-ene-l-carboxylic acid methyl ester (5.09 g, 86%) as a pale yellow oil. Subsequent preparations of 5-azido-4-hydroxy-3-methoxymethoxy-cyclohex-l-ene-l-carboxylic acid methyl ester provided material which was of sufficient purity to use in the next step without further purification. 

C—C—O—C+N. The formation of oxazoles from a-acyloxy ketones and ammonium salts was discovered in 1937 when it was found that treatment of benzoin benzoate with ammonium acetate in hot acetic acid gave triphenyloxazole in excellent yield. It has been shown that the reaction proceeds by way of intermediate enamines (equation 113). The synthesis is quite general and it is only.limited by the difficulty of obtaining the starting keto esters, particularly formates. The latter are probably intermediates in the preparation of cycloalkenooxazoles from acyloins and formamide in hot sulfuric acid (equation 114). Another variation is to heat a mixture of an a-bromo ketone, the sodium salt of a carboxylic acid and ammonium acetate in acetic acid (equation 115). 

A new type of latent-active glycosyl donors, 2 -carboxybenxyl glycosides and their benzyl esters, have been recently introduced [62-64]. The active carboxylic acids are readily available from the latent benzyl esters by catalytic hydrogenation in the presence of ammonium acetate. In an example [62] shown in Scheme 5.24 the latent mannoside (136) was glycosylated with the active donor (135) to provide exclusively the p-linked disaccharide (137) in excellent yield. The latent... 

Application of the Davidson oxazole synthesis to products of the Passerini reaction has expanded the usefulness of this well-known route <91LAll07>. The a-acyloxy ketones or a-acyloxy -keto esters employed in the Davidson synthesis are not readily available. However, the use of arylglyoxals as the carbonyl component of the Passerini reaction, along with cyclohexyl isocyanide and carboxylic acids, gives a wide variety of iV-cyclohexyl-2-acyloxy-3-aryl-3-oxopropionamides (151). Reaction of these intermediates with ammonium formate in acetic acid affords A -cyclohexyl-2,4-diaryl-5-oxazolecarboxamides (152) in fair yields (Scheme 69). 

A new type of copolymer resist named ESCAP (environmentally stable chemical amplification photoresist) has recently been reported from IBM [163], which is based on a random copolymer of 4-hydroxystyrene with tert-butyl acrylate (TBA) (Fig. 37), which is converted to a copolymer of the hydroxystyrene with acrylic acid through photochemically-induced acid-catalyzed deprotection. The copolymer can be readily synthesized by direct radical copolymerization of 4-hydroxystyrene with tert-butyl acrylate or alternatively by radical copolymerization of 4-acetoxystyrene with the acrylate followed by selective hydrolysis of the acetate group with ammonium hydroxide. The copolymerization behavior as a function of conversion has been simulated for the both systems based on experimentally determined monomer reactivity ratios (Table 1) [164]. In comparison with the above-mentioned partially protected PHOST systems, this copolymer does not undergo thermal deprotection up to 180 °C. Furthermore, as mentioned earlier, the conversion of the terf-butyl ester to carboxylic acid provides an extremely fast dissolution rate in the exposed regions and a large... 

The ammonium formate in formic acid procedure has rendered possible the first preparation of isomeric 4,5-disubstituted oxazoles.03101 Bredereck, Gompper, and Reich101 have reported the anomalous behavior of certain long-chain a-bromo ketones a single a-bromo ketone on reaction with ammonium formate in formic acid gives a mixture of two isomeric oxazoles. Refluxing of a-bromo ketones or of a-chloro-/3-keto esters with ammonium acetate in acetic acid results in the formation of substituted 2-methyl-oxazoles.40 102 Ethyl a-chloroacetoacetate on heating with ammonium carbonate or formamide in formic acid yields 4-methyloxazole-5-carboxylic ester.40 103... 

Although the combined additive phosphonylation and esterification of an a,j5-unsatu-rated carboxylic acid by a trialkyl phosphite can thus easily, although not necessarily accurately, be envisaged, that of a similarly unsaturated ester, nitrile, or amide is perhaps not so readily apparent. Harvey showed that successful reaction between triethyl phosphite and such a substrate (Scheme 43) occurs in a protic medium. In this respect, the reactions proceed faster in methanol than in ethanol, but reactions are, in general, (including those of structurally analogous unsaturated ketones) much cleaner and faster when carried out in phenol, and also afford much higher yields in this solvent. It has also been shown that ammonium salts will also act as a proton source to allow completion of addition without alkylation. The later Russian workers used acetic acid with successful results ... 

Following the original report that the oxazoline carboxylic acid 7.5.12 can serve as an excellent side chain precursor 281), several syntheses of this compound have been reported. Thus racemic oxazoline was prepared from protected cinnamyl alcohol by addition of phenyl-selenyl triflate and azide ion to give the adduct 7.5.9, which was then converted to oxazoline 7.5.10 and ester 7.5.11 282). A similar but more efficient route used diphenyldiselenide and ammonium persulfate to give the racemic oxazoline 7.5.10 in 95% yield from cinnamyl acetate 283). 

Carboxylic acid methyl esters. A methanolic soln. of oleanolic acid containing phenolphthalein as indicator titrated with a soln. of tetramethylammonium hydroxide in the same solvent, which is then removed by distillation, and the residual tetramethylammonium salt heated under reduced pressure with distillation of the resulting trimethylamine -> methyl oleanolate. Y 83%. F. e. s. V. Prelog and M. Piantanida, H. 244, 56 (1936) by gas-diromatography s. A. S. Hyman, J. Chromatogr. 45, 132 (1969) ethers from quaternary ammonium hydroxides and acetates cf. J. MacGee and K. G. Allen, Steroids 16, 19 (1970). 

Probably the most obvious method for the eationie polymerization of NVK involves treatment of the monomer with aeids. So NVK ean be polymerized by hydrochloric acid [428], perchloric acid [429,430], ammonium perchlorate [431] and several other Bronsted acids [432]. Due to the nueleophilieity of NVK, even relatively weak carboxylic acids will cause polymerization [433]. In diehloroethane, a solvent of medium polarity, oligomers bearing a terminal acetate ester were isolated from the reaetion of NVK with an excess of acetic acid [434]. This suggests that proton addition to the p carbon of the monomer is followed by the addition of the eounterion to the a earbon, forming a polarized ester. The lability of the ester linkage was demonstrated by the rapid hydrolysis of the monomeric adduct in the presence of atmospherie moisture. 

General procedure for the synthesis of 1,4,7,8-tetrahydro-2,7,7-trimethyl-4-aryl-5(6H)-oxo-quinolin-3-carboxylic acid alkyl ester (5). A mixture of aldehyde (1 2 mmol), dimedone (2 2 mmol), p-ketoester (3 2 mmol), and ammonium acetate (4 3 mmol) was thoroughly mixed in a mortar followed by grinding till the completion of reaction as indicated by TLC (12-45 min). The resultant mass was washed with water to remove any unreacted ammonium acetate and was air-dried to give a crude product which on recrystallization from ethanol afforded the pure desired compound (5) in excellent yield (80-95%). 

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