Esters open-chain

A specially interesting case of the blocked carbonyl compound is the lactone or cyclic ester. Open-chain esters do not give aldol reactions they prefer a different reaction that is the subject of the next chapter. But lactones are in some ways quite like ketones and give unsaturated carbonyl products under basic catalysis. Enolization is unambiguous because the ester oxygen atom blocks enolization on one side. 

Unlike carboxylic esters, open-chained S-alkyl thiocarboxylates cannot be obtained by direct proton-catalyzed esterification. Whereas thiocarboxylic acids react with alcohols to form esters as expected, thiol esters are formed on reaction of carboxylic acids with thiols, but the equilibrium is shifted towards the educts and the reaction is not useful for synthetic purposes. Therefore, activation is necessary and several methods have been developed to meet this requirement. 

Regioselectivity becomes important, if unsymmetric difunctional nitrogen components are used. In such cases two different reactions of the nitrogen nucleophile with the open-chain educt may be possible, one of which must be faster than the other. Hydrazone formation, for example, occurs more readily than hydrazinoLysis of an ester. In the second example, on the other hand, the amide is formed very rapidly from the acyl chloride, and only one cyclization product is observed. 

Macrocyclic peptides and depsipeptides ( macrocyciic peptides with amide and ester linkages) are important natural compounds. They have been synthesized in low yield from open-chain precursors by DCC treatment at high dilution (E. SchrSder, 1963 M.M. Shemyakin,... 

Five-ring lactone corresponding open-chain esters 1780-1760 ... 

CLAISEN - GEUTER - OIECKMANN Ester condensation Synthesis ot open chain or cyclic p keloesters by aldol type condensation... 

Table 7.5. Open-chained esters, ketones, and carbamates ...

Chapter 7 Open-chained materials of all descriptions including nitrogen, sulfur, ester, etc. 

The initial observation that menthone reacts with amyl nitrite in the presence of base to give a good yield of an open-chain oximino ester was not expanded for synthetic purposes until Woodward almost forty years later utilized this reaction for the cleavage of a 7-keto-decahydroisoquinoline in the course of his total synthesis of quinine. 

There has been new information on the products of photolysis of derivatives of compound 1. Low temperature irradiation of the ester 254 gives a ketene (93JACS8621) the isolation of an isomeric ketene from a 3-pyridyldiazo ester suggests the involvement of the open chain form 255. Photolysis of the 3-phenyl derivative 256 in the presence of cyclopentadiene gives exo and endo cyclopropanes and a dipyridylstilhene, suggesting the intermediacy of the carhene 257 (99JOC6635). 

The oxidation of ethers to esters according to the reaction offers many possibilities for the modification of functionality in open chain or cyclic systems. An example is the... 

We ve discussed only open-chain compounds up to this point, but most organic compounds contain rings of carbon atoms. Chcysanthemic acid, for instance, whose esters occur naturally as the active insecticidal constituents of chrysanthemum flowers, contains a three-membered (cyclopropane) ring. 

Most heterocycles have the same chemistry as their open-chain counterparts. Lactones and acyclic esters behave similarly, lactams and acyclic amides behave similarly, and cyclic and acyclic ethers behave similarly. In certain cases, however, particularly when the ring is unsat lira ted, heterocycles have unique and interesting properties. 

An inspection of Tables 1 and 2 shows that appropriate solvents for lithium batteries mainly belong to classes 6 and 7 and include cyclic (EC, PC) and open-chain (DMC, MEC, DEC, MPC) esters and ethers (DIOX, DME, THF) as well as inorganic sulfur compounds (S02, SOCl2). These sulfur compounds are mainly used as liquid cathode materials, simultaneously serving as solvents (S02C12, SOCl2) or cosolvents (S02) in primary or secondary lithium batteries. Recent developments of solvents include... 

The addition of (Z)-3-(alkylamino)-2-butenoic acid esters to nitroalkenes derived from open-chain sugars gave a 50 50 mixture of diastereomeric products 32. The reaction of chiral 2-sub-stituted l-(2-nitroethenyl)pyrrolidines with zinc enolates of 3-substituted tetrahydro-2//-pyran-2-oncs in 1,2-dimethoxyethane at — 78 °C afforded the corresponding 3,3-disubstituted products in 82-96% ee via an addition-elimination process33. The stereochemical course of the reaction was determined by chemical correlation of (S)-( )-3-ethyltetrahydro-3-(2-ni-troethenyl)-2//-pyran-2-one with ( + )-quebrachamine. 

Reactions. PE readily forms esters with organic and inorganic acids (Refs 9, p 157 13, pp 54, 212 246) and cyclic as well as open chain acetals and ketals (Refs 9, p 195 13, p 141). Some of these prods are used in expls, while others... 

Although a maj ority of research activities were dedicated to cycloketone converting BVMOs, the recently discovered novel MOs also enable stereoselective oxidation of noncyclic ketones to esters. An aliphatic open-chain monooxygenase (AOCMO) from Pseudomonas Jluorescens DSM 50106 displays stereoselective biooxidation of terminal acyl-groups in proximity to hydroxyls (Scheme 9.23). The biooxidation gives acetic... 

No compound other than the methyl ester of N-benzoyl-Lphenylalanine, 33, is an obvious choice for an open-chain analog of the locked substrate 25 but D-24, on the other hand, may be a locked analog of either N-benzoyl-D-alanine methyl ester 34 or of N-formyl-D-phenylalanine methyl ester 35 (75). If 24 is an analog of 34 rather than 35, the comparison of the two locked analogs made in Section V.B. is not valid the phenyl of 24 would then correspond to the benzoyl phenyl of 34. 

N-Benzoyl-Lalanine methyl ester is in turn about eight times more reactive than is its D enantiomer). The open-chain compounds may not bind to the enzyme in the same manner, however, as does the locked substrate. The conformation around the amido bond of the open-chain compounds, for example, can be transoid rather than cisoid (81). In addition, if equatorial 24 is considered to be the reactive conformer for both the Dand L enantiomers, and if the alanine methyl group is attracted to the hydrophobic aromatic binding subsite, then structures 34 and 38 would result. The L enantiomer of N-benzoyl-phenylalanine methyl ester 38 in this representation has approximately the same conformation as equatorial L-24. But attraction of the methyl of the D enantiomer to the location occupied by the methyl group of the L enantiomer causes the carbomethoxy group to move from the position it occupies in D-24. 

The p a values of two systems with two intra-annular COOH groups have been measured. In Cram s study (Bell et al., 1982), the macrocyclic diacid [36] and an open-chain monomeric analogue [37] had almost identical pK values (see Table 18). In contrast, Gennari s compound [38], which contains two intra-annular COOH groups and in addition two"ethyl ester groups, has a different acidity from that of the analogues [39] and [40], as shown in Table 19 (Gennari et al., 1992). But in both systems, the difference Ap a between pK i and p a2 was comparable (ApA a [36] = 1.7, Ap/La[38] = 1.5). The increase from p ai to P a2 may occur for two... 

Mono- and dilithio derivatives of p-tosylmethyl isocyanide 297a were shown to display interesting reactions. Reaction of the monoanion with unsaturated esters was shown to give pyrrole derivatives . Dianion 297b was found to add to the carbon-nitrogen double bonds of isoquinoline, quinoline and quinoxaline affording compounds 298, 299 and 300, respectively. In the reactions with pyridine iV-oxide and pyridazine iV-oxide, unstable open-chain products 301 and 302 were obtained . 

Waldmann used (R) and (5>aminoacid methyl esters and chiral amines as chiral auxiliaries in analogous aza-Diels-Alder reactions with cyclodienes.111 The diastereoselectivity of these reactions ranged from moderate to excellent and the open-chain dienes reacted similarly. Recently, the aza-Diels-Alder reaction was used by Waldmann in the asymmetric synthesis of highly functionalized tetracyclic indole derivatives (Eq. 12.45), which is useful for the synthesis of yohimbine- and reserpine-type alkaloids.112... 

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