Esters, thio

The Pd-catalyzed hydrogenoiysis of acyl chlorides with hydrogen to give aldehydes is called the Rosenmund reduction. Rosenmund reduction catalyzed by supported Pd is explained by the formation of an acylpalladium complex and its hydrogenolysis[744]. Aldehydes can be obtained using other hydrides. For example, the Pd-catalyzed reaction of acyl halides with tin hydride gives aldehydes[745]. This is the tin Form of Rosenmund reduction. Aldehydes are i ormed by the reaction of the thio esters 873 with hydrosilanes[746,747]. 

Diaryl disulfides and diselenides add to alkynes to afford the (Z)-l, 2-bis(ar-ylthio)alkenes 193 and (Z)-l,2-bis(arylseleno)alkenes 194. Under CO pressure, carbonylative addition takes place to give thio esters and the selenoketones 195[I07], The selenoketones are converted into the /J-seleno-a, 3-unsaturated aldehydes 196 by Pd-catalyzed hydrogenolysis with HSnBu3[108,109],... 

In the synthesis of ceftazidime (40) (Fig. 8), the protected, preassembled arninothiazole side chain [68672-66-2] (60) is coupled to a protected 7-ACA first and the C-3 displacement step carried out last. By way of contrast, in the synthesis of ceftriaxone (39) (Fig. 9), the preformed C-3 substituent is introduced onto the cephalosporin nucleus in the first step and then the acyl-amino side chain is introduced. This last step is noteworthy for two reasons in that it demonstrates the use of an activated thio ester in the coupling step and that no protecting group chemistry is requited (192,193). 

One of the C(15) epimeric thio esters (B) cyclizes more slowly than the other (by a factor of 03. 15) due to steric repulsions involving the methyl group at C(15). After lactonization, the uncyclized diastereomer was recovered and used for the synthesis as following. 

Substituted-4-hydroxy-6-methylpyrimidines are formylated in the 5-position when the 2-substituent (e.g. NH2, OH) is sufficiently electron releasing. The related 4-mercapto compounds gave only the ortho-thio-esters. ... 

The Michael reaction occurs with a variety of a,/3-unsaturated carbonyl compounds, not just conjugated ketones. Unsaturated aldehydes, esters, thio-esters, nitriles, amides, and nitro compounds can all act as the electrophilic acceptor component in Michael reactions (Table 23.1). Similarly, a variety of different donors can be used, including /3-diketones, /3-keto esters, malonic esters, /3-keto nitriles, and nitro compounds. 

Acyl halides react with thiols, in the presence of zinc, to give the corresponding thio ester. ... 

The final example of a domino process under high pressure, to be discussed in this chapter, is a combination of a Horner-Wittig-Emmons (HWE) reaction with a Michael addition developed by Reiser and coworkers [5]. Hence, reaction of a mixture of an aldehyde such as 10-18, a phosphonate 10-19 and a nucleophile 10-20 in the presence of triethylamine at 8 kbar led to 10-21. By this method, (3-amino esters, 3-thio esters and 3-thio nitriles can be prepared in high yield (Scheme 10.4). Many of these transformations do not occur under standard conditions, thereby underlining the importance of high pressure in organic chemistry. 

In all cases, dithio-phosphorus acids can be liberated from their alkali-metal salts by reacting them with acids such as HC1. Thio-ester derivatives of the dithio-phosphorus acids can be synthesised via reaction of the acids themselves with an alcohol or phenol (Equation 26) or from reaction of their alkali-metal salt with an alkyl halide (Equation 27). 

It has been reported that diiron acyl complexes (564) undergo stereo- and regioselective 1,3- cycloadditions with a variety of nitrones (Scheme 2.260). These complexes are then oxidatively converted to synthetically useful thio esters (769). 

In most conjugations, it is the cofactor that is activated, but in amino acid conjugation it is the substrate that is activated, first by reacting with ATP to form an AMP conjugate, which is further converted to a CoA thio ester as shown in Figure 7.13. 

Use me thio esters (-C02SR ) obtained from me ROCO-Peptide-SR -linker-resins assembled by solid-phase synthesis (see Section 7.10).74... 

H Hojo, S Aimoto. Polypeptide synthesis by use of an 5-alkyl thio ester of a partially protected segment. Synthesis of the DNA-binding domaine of c-Myb protein (142-1193)-NH2. Bull Chem Soc Jpn 64, 111, 1991. 

The subsequent cleavage of the thio-ester succinylCoA into succinate and coenzyme A by succinic acid-CoA ligase (succinyl CoA synthetase, succinic thiokinase) is strongly exergonic and is used to synthesize a phosphoric acid anhydride bond ( substrate level phosphorylation , see p. 124). However, it is not ATP that is produced here as is otherwise usually the case, but instead guanosine triphosphate (CTP). However, GTP can be converted into ATP by a nucleoside diphosphate kinase (not shown). 

Reduction of Ortho Esters, Thio Esters and Dithio Esters... 

Figure 13.17 General structure of phosphoric and thiophosphoric acid (thio)esters. Note that often Ri = R2 = CH3 or C2H5.

In Lipmann s original scheme group Y was visualized as adding to a carbon-carbon double bond to initiate the sequence. Isotopic exchange reactions ruled out the possibility that either ADP or P might serve as Y, but it was attractive to think that a bound phosphate ion, e.g., in a phospholipid or coenzyme, could be involved. Y B of Fig. 18-12 would be similar in reactivity to an acyl phosphate or thio-ester. However, whatever the nature of Y B, part of group Y would be left attached to B after the transfer of Y to X. For example, if Y were Y OH... 

Oxoacyl-CoA transferase (see fig. 18.8) is involved in the transfer of a CoASH from succinyl-CoA to acetoacetate to produce succinate and aceto-acetyl-CoA. A cursory examination of this reaction suggests a simple transfer of the CoA moiety. However, it is soon realized that the loss of an oxygen by the acetoacetate and the gain of an oxygen by the succinyl group present a dilemma. Produce a rational mechanism that explains the preservation of the thio-ester energy and solves this dilemma. Hint Consider a succinyl phosphate intermediate. 

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