Esters, carboxylic acid cyclic

Monobasic carboxylic acids with an a-methyl group Esters of aliphatic dibasic carboxylic acids Cyclic sulfides... 

The direct fluorination with elemental fluorine at — 78 "C of trimethylsilyl enol ethers derived from diketones results in the formation of the corresponding monofluoro diketones 11 in moderate yield. The trimethylsilyl ethers from cyclic diketones undergo smooth fluorination to give the enol forms, c.g. 12, and not the keto forms.Higher yields are generally observed for the analogous reactions of silyl derivatives of esters, carboxylic acids, malonates, dimethyl amides and lactones (Table 4). ... 

If the molecule is indeed bent out of a plane the nitro substituent should produce the potentiality for molecular asymmetry. Hence the nitro derivative was treated with p-boronobenzoic acid in benzene under a water separator to yield the cyclic boronate ester carboxylic acid (8). a derivative directly suitable for optical resolution. As a carboxylic acid. (8) gave a crystalline salt with quinine which, after four recrystallizations (aD — 37.4°), liberation of the organic acid, and hydrolysis gave optically active nitroglycol (6), X = NO,. Lead tetraacetate cleavage of the dextrorotatory (6), X = N02. gave optically active (5), X = NO,. the racemization of polarimetry in a chloroform solution. 

A carbonyl group is a carbon double-bonded to an oxygen an acyl group is a carbonyl group attached to an alkyl or aryl group. Acyl halides, acid anhydrides, esters, and amides are called carboxylic acid derivatives because they differ from a carboxylic acid only in the nature of the group that has replaced the OH group of the carboxylic acid. Cyclic esters are called lactones cyclic amides are lactams. There are symmetrical anhydrides and mixed anhydrides. 

S.2 Copolymer Formation by Carboxylic Acid + Cyclic Ortho Ester or Epoxide Reaction... 

Table 5.33 PEST/PO blends copolymer formation by carboxylic acid + cyclic ortho ester or ...

Lactones, which may be regarded as cyclic or inner esters, react similarly. Anhydrides of carboxylic acids also react with hydroxylamine to form hydroxamic acids ... 

Hydroxy acids compounds that contain both a hydroxyl and a carboxylic acid function have the capacity to form cyclic esters called lactones This intramolecular esterification takes place spontaneously when the ring that is formed is five or six membered Lac tones that contain a five membered cyclic ester are referred to as 7 lactones, their six membered analogs are known as 8 lactones... 

During electrochemical fluorination retention of important functional groups or atoms in molecules is essential. Acyl fluorides and chlorides, but not carboxylic acids and anhydrides (which decarboxylate), survive perfluorination to the perfluorinated acid fluorides, albeit with some cyclization in longer chain (>C4) species [73]. Electrochemical fluorination of acetyl fluoride produces perfluoro-acetyl fluoride in 36-45% yields [85]. Electrochemical fluorination of octanoyl chloride results in perfluorinated cyclic ethers as well as perfluorinated octanoyl fluonde. Cyclization decreases as initial substrate concentration increases and has been linked to hydrogen-bonded onium polycations [73]. Cyclization is a common phenomenon involving longer (>C4) and branched chains. a-Alkyl-substituted carboxylic acid chlorides, fluorides, and methyl esters produce both the perfluorinated cyclic five- and six-membered ring ethers as well as the perfluorinated acid... 

Electrochemical fluonnation ot N,N dialkylammo-substituted carboxylic acids as their methyl esters produces the analogous perfluonnated tertiary amine carboxylic acid derivatives in 18-30% yields as well as cyclic amine ethers [JOO]... 

Reaction of 9,10-difluoro-7-oxo-2,3-dihydro-7//-pyrido[l, 2,3- e]-1,4-ben-zothiazine-6-carboxylic acid and its ethyl ester with B(OH)3 in AC2O in the presence of ZnCl2 afforded 6-[(diacetoxyboryl)oxycarbonyl] derivative 323 (R = OAc)], which was reacted with primary and cyclic amines to give 10-amino-9-fluoro-7-carboxylic acid derivatives 324 (97MI41, 98MI30). 6-[(Difluoroboryl)oxycarbonyl derivative 323 (R = F) was obtained from ethyl 9,10-difluoro-7-oxo-2,3-dihydro-7//-pyrido[l,2,3- fe]-l,4-benzothiazine-6-carboxylate with BF3-THF complex. Reaction of 323 (R = F) and 1-methylpiperazine in DMF at 50-60 °C and subsequent acidic hydrolysis afforded 7 (97MI1). 

Esters undergo the same kinds of reactions that we ve seen for other carboxylic acid derivatives, but they are less reactive toward nucleophiles than either acid chlorides or anhydrides. All their reactions are equally applicable to both acyclic and cyclic esters, called lactones. 

Fischer s original method for conversion of the nitrile into an aldehyde involved hydrolysis to a carboxylic acid, ring closure to a cyclic ester (lactone), and subsequent reduction. A modern improvement is to reduce the nitrile over a palladium catalyst, yielding an imine intermediate that is hydrolyzed to an aldehyde. Note that the cyanohydrin is formed as a mixture of stereoisomers at the new chirality center, so two new aldoses, differing only in their stereochemistry at C2, Tesult from Kiliani-Fischer synthesis. Chain extension of D-arabinose, for example, yields a mixture of D-glucose and o-mannose. 

Eq. (3), with lithium diisopropylamide (LDA) to a lithiospecies and in its subsequent reaction with C02 affording via the corresponding 4-carboxylic acid its ethyl ester 59. In the alternative version perchlorate 48e is electro-chemically reduced in acetonitrile to an anionic species that was converted either to a 3 1 mixture of isomers 56 (R = f-Bu) and 60 or to 4//-thiopyran 56 (R = PhCH2) with f-BuI or PhCH2Br, respectively (90ACS524). The kinetics of the benzylation procedure was followed by cyclic voltammetry [88ACS(B)269]. 

The mechanism of oxidation probably involves in most cases the initial formation of a glycol (15-35) or cyclic ester,and then further oxidation as in 19-7. In line with the electrophilic attack on the alkene, triple-bonds are more resistant to oxidation than double bonds. Terminal triple-bond compounds can be cleaved to carboxylic acids (RC=CHRCOOH) with thallium(III) nitrate or with [bis(trifluoroacetoxy)iodo]pentafluorobenzene, that is, C6F5l(OCOCF3)2, among other reagents. 

N-Silylated peptide esters are acylated by the acid chloride of N-Cbo-glycine to N-acylated peptide bonds [11]. Likewise, acid chlorides, prepared by treatment of carboxylic acids with oxalyl chloride, react with HMDS 2 at 24°C in CH2CI2 to give Me3SiCl 14 and primary amides in 50-92% yield [12]. Free amino acids such as L-phenylalanine or /5-alanine are silylated by Me2SiCl2 48 in pyridine to 0,N-protected and activated cyclic intermediates, which are not isolated but reacted in situ with three equivalents of benzylamine to give, after 16 h and subsequent chro-... 

This reagent combination also converts carboxylic acids to acyl chlorides (see Section 3.4.1). The mechanistic basis for the special effectiveness of benzotriazole has not yet been determined, but it seems likely that nucleophilic catalysis is involved. Sulfinyl ester intermediates may be involved, because Z-2-butene-l,4-diol gives a cyclic sulfite ester with one equivalent of reagent but the dichloride with two equivalents. 

The highly ordered cyclic TS of the D-A reaction permits design of diastereo-or enantioselective reactions. (See Section 2.4 of Part A to review the principles of diastereoselectivity and enantioselectivity.) One way to achieve this is to install a chiral auxiliary.80 The cycloaddition proceeds to give two diastereomeric products that can be separated and purified. Because of the lower temperature required and the greater stereoselectivity observed in Lewis acid-catalyzed reactions, the best diastereoselectivity is observed in catalyzed reactions. Several chiral auxiliaries that are capable of high levels of diastereoselectivity have been developed. Chiral esters and amides of acrylic acid are particularly useful because the auxiliary can be recovered by hydrolysis of the purified adduct to give the enantiomerically pure carboxylic acid. Early examples involved acryloyl esters of chiral alcohols, including lactates and mandelates. Esters of the lactone of 2,4-dihydroxy-3,3-dimethylbutanoic acid (pantolactone) have also proven useful. 

The subjects of this section are two reactions that do not actually involve carbo-cation intermediates. They do, however, result in carbon to carbon rearrangements that are structurally similar to the pinacol rearrangement. In both reactions cyclic intermediates are formed, at least under some circumstances. In the Favorskii rearrangement, an a-halo ketone rearranges to a carboxylic acid or ester. In the Ramberg-Backlund reaction, an a-halo sulfone gives an alkene. 

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