Thiol acids formation

Hydroxy and 7-thiol acids (32 Z = 0, S) usually cyclize spontaneously to give lactones and thiolactones (33). 7-Amino acids (32 Z=NH) require heating to effect lactam formation (33 Z = NH). 

The reaction cascade induced by treatment with acids. Formation of 5H-pyriodo [l, 2 4,5] [1,2,4] thiadiazino benzimidazole-13-ium salts and their reactions with thiols./. Org. Chem.,... 

Pyrrolidine (39 Z = NH) and thiolane (39 Z = S) can be prepared from tetramethylene dibromide 38, and tetrahy-drofuran (39 Z = O) is obtained from the diol 40. -Hydroxy and -thiol acids (41 Z = O, S) usually cyclize spontaneously to give lactones and thiolactones 42. -Amino acids (41 Z = NH) require heating to effect lactam formation (42 Z = NH) (Scheme 31). 

Methods available before 1971 for the preparation of thiol esters are briefly summarized in a review article.4 Since then, several newer techniques have been developed, to meet a certain set of criteria required for recent synthetic operations. This development may be summarized as follows. Whenever an acid chloride is available, the reaction of the T1(I) salt of a thiolate of virtually any kind, including alkane-, benzene-, 2-benzothiazoline-, and 2-pyridinethiol, proceeds efficiently and near-quan-titatively. However, if selective thiol ester formation in the presence of hydroxy or other functional groups in the same molecule is required, three main procedures are available. First, reaction of an acid (1), with... 

Other methods that can be used to prepare thiol esters from carboxylic acids include the use of aryl thiocyanates,12 thiopyridyl chloroformate,13 2-fIuoro- V-methylpyridinium tosylate,14 1-hydroxybenzotriazole, 5 and boron thiolate.16 Direct conversion of 0-esters to 5-esters can also be effected via aluminum and boron reagents.17 However, the applicability of these 1217 and other more recent methods18 to the selective thiol ester formation discussed above has not been clearly defined. 

Therefore, the kinetics and the product yields of isomerization and thiol adduct formation for a variety of Z- and ii-monounsaturated fatty acid (MUFA) esters were studied. The reactions were initiated by continuous °Co y-irradiation of N20-saturated f rf-butanol solutions containing -mercaptoethanol and MUFA esters. The time-dependent isomerizations and thiol additions were analyzed on the basis of the radiation chemical yields of radicals and established rate data. The rate constants for the reversible RS addition, within experimental error, do not depend on the double bond position in the alkyl chains vide Table 6). 

The construction of the naturally derived narbomycin and tylosin-aglycones by Masamune and coworkers employ identical methodology for seco-acid formation. In each case, Peterson alkenadon of a functionalized aldehyde (not shown) and the silyl ketones (96 R = SiMes Scheme 36) or (99 Scheme 37) efficiently introduced the required ( )-a,3-unsaturation. Silyl ketone formation is accomplished in each case through cuprate acylation by an activated carboxylic acid derivative. Formation of an acid chloride was not possible in the sensitive tylosin-aglycone intermediate however, selective acylation of the silylcuprate proceeded at the pyridyl thiol ester moiety of (98) and not with the r-butyl thiol ester. In a related investigation, (97), an advanced intermediate for 6-deoxyerythronolide B, was obtained from (95) via addition of lithium diethylcuprate to the acid chloride (84% yield). In all the above cases, no addition was observed at the f-butyl thiol ester. 

IV. Thiol-ester Formation in a-Keto Acid Oxidation. 196... 

The thiol formates have CH vibrations which absorb at 2835-2825 cm" (CH stretch), 1345-1340 cm (CH deformation), and 2680-2660 cm (deformation overtone). The thiol acids in solution absorb at 2585-2565 cm (SH stretch) and at 837-828 cm" (SH in-plane deformation). ... 

A variety of terminal functional groups and their chemical transformations on SAMs have been examined for example, (i) olefins—oxidation [23,24,131,132], hydroboration, and halogenation [23,24] (ii) amines—silyla-tion [145,146], coupling with carboxylic acids [22,146], and condensation with aldehydes [22,147] (iii) hydroxyl groups—reactions with anhydrides [148,149], isocyanates [150], epichlorohydrin [151], and chlorosilanes [152] (iv) carboxylic acids—formation of acyl chlorides [153], mixed anhydrides [154], and activated esters [148,155] (v) carboxylic esters—reduction and hydrolysis [156] (vi) thiols and sulfides—oxidation to generate disulfides [157-159] and sulfoxides [160] and (vii) aldehydes—condensation with active amines [161], Nucleophilic... 

Thus, three theories had been developed and each had difficulties formation of metal thiols did not fit thermodynamics, adsorption of ions did not fit charge requirements, and adsorption of thiol acids did not fit stability criteria. 

Thiol-acids and Thiol-est. —Most of the references in the recent literature dealing with these classes of compound from the point of view of new chemistry concern thiol-esters, and apart from a study of the formation of diacyl sulphide using DCCI and reaction with arene oxides [(13) -> (14)], the current literature on... 

Although a variety of oxidizing agents are available for this transformation it occurs so readily that thiols are slowly converted to disulfides by the oxygen m the air Dithiols give cyclic disulfides by intramolecular sulfur-sulfur bond formation An example of a cyclic disulfide is the coenzyme a lipoic acid The last step m the laboratory synthesis of a lipoic acid IS an iron(III) catalyzed oxidation of the dithiol shown... 

Herein the focus is on SAMs of trichlorosilanes and thiols. SAMs of carboxyUc acids are important as a connection between the LB and self-assembly techniques, but studies of their formation and stmcture have been relatively limited. SAMs of carboxyUc acids on AI2O2, AgO, and CuO have also been carried out (113—124). 

Alcohol Substitution. In the early period of normal thiol production, the normal alcohols were utilized as feedstocks. The use of a strong acid catalyst results in the formation of a significant amount of secondary thiol, along with other isomers resulting from skeletal isomerization of the starting material. This process has largely been replaced by uv-initiation because of the higher relative cost of alcohol vs alkene feedstock. 

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