5- thiobenzoates, synthesis

A procedure, which has been used successfully for the synthesis of dialkyl thioethers from thioacetamide has been extended to the preparation of a range of 5-alkyl thiocarboxylic esters [35] (Table 4.20). The intermediate 5-acyl ethaniminium salt (Scheme 4.14) is not stable and is converted directly into the 5-alkyl thioester. The choice of catalyst affects the yield of the thioesters. Thus, 5-n-octyl thiobenzoate... 

The synthesis of four out of eight possible stereoisomers of 3-methyllanthionine [(25,35,67 ), (25,37 ,67 ), (25,35,65), (25,37 ,65)] has been achieved using the reaction of Z-protected 3-methyl-D-cysteine with d- or L-3-chloroalanine in yields of 35—53% J64 The methyl-D-cys-teine stereoisomers were obtained by two routes. Firstly from (25,35)-threonine via O-tosylation and subsequent inversion of configuration by nucleophilic attack with thiobenzoic acid. The resulting derivative was debenzoylated and oxidized to the respective cystine derivative prior to the reduction with Zn/HCl to give the eryt/u-o-3-methyl-D-cysteine... 

Historically, this represents the first thiophene synthesis, when Laurent obtained tetraphenylthiophene by heating polymeric thiobenzaldehyde in 1844. Almost any aromatic methyl derivative can be converted to tetraphenylthiophene, which is thermodynamically the most stable thiophene, by heating with sulfur. Toluene, phenylacetic acid, benzyl alcohol, benzyl sulfide or disulfide, benzyl sulfonate or even sodium thiobenzoate have been converted to tetraphenylthiophene under these conditions (52HC(3)l). 

Cleavage of allylamines is rather difficult. However, unexpectedly the allylamine 340 is deprotected by allyl transfer to dimethylbarbiturate (341) [158] or to 2-thiobenzoic acid using DPPB as a ligand [159]. The 2-thiobenzoic acid method has been applied to indole synthesis [160], Allylamines are also cleaved with Pd/C in EtOH in the presence of methanesulfonic acid [161] or with Ni(dppp)Cl2 [162], Thus diallylamine (339) can be regarded as protected ammonia. 

A synthesis of a-lipoic acid and derivatives has been reported. The pendant alkene of complex (111) was transformed to a primary alcohol (112) via hydroboration-oxidation sequence. Mitsunobu coupling of (112) with thiobenzoic acids to give (113), followed by desilylation and nucleophilic substitution again employing thiobenzoic acid gave the advanced intermediate (114) (Scheme 169). 

Kim has also studied the corresponding acylation of homocuprates by S-(2-pyridyl) thioates, discussed earlier in the context of total synthesis of monensin and erythronolide A (Sections 1.13.2.2 and 1.13.3.2). Under the standard anaerobic conditions necessary for cuprate formation, good yields of ketones could be derived from acylation of lithium dimethylcuprate (or lithium dibutylcuprate) by S-(2-pyridyl) thiobenzoate and other simple S-(pyridyl) thiol esters (equation 71). Interestingly, if the homocuprate is intentionally placed under an oxygen atmosphere before acylation and then reacted with the S-(2-pyridyl) thioate in oxygen at -78 C, one obtains good yields of the ctnresponding ester (equation 72). 

The above-mentioned (9-deoxyribosyl thiobenzoate (c/. equation 39) was obtained from 1,5-protected deoxyribose and phenyl dithiobenzoate. ° Also vinyl arenecarbodithioates were shown to be applicable for the synthesis of thioxoesters." ... 

Diphenylamines containing substituents other than carboxyl can act as precursors of acridones, though not necessarily via a carbocation intermediate and novel examples include the thiobenzoate (32) (J. Martens, K. Fraefcke and U. Schulze. Synthesis, 1976, 532) and the Schiff s base (33). 

There has been only one example of the synthesis of (r] -cyclopentadienyl)-bis(thiobenzoato)tantalum 20, which was achieved by the reaction of Ta(Cp)2X2 (X=C1, Br, I) with thallium thiobenzoate [110]. The molecular structure of 20 is a normal, bent sandwich geometry where the two thiocarboxylato ligands are planar and are monodentate through the sulfur atom (for bond distances, see Table 2) [110]. 

In 1966, King reported the first synthesis of thiocarboxylato iron complex CpFe(CO)2(PhCOS), achieved by treating [CpFe(CO)2]2 with thiobenzoic acid... 

Analogous to the synthesis of l,4-benzodioxepin-5-ones, the benzoxathiepinones (166) were prepared by the reaction of ethyl 2-thiobenzoates with chlorohydrin and glycerol chlorohydrin and cyclization of intermediate (165) (Scheme 17) <75BSF277>. The sodium borohydride reduction of bienzoxathiepinone (167) has also been studied <82NJC149>. 

N-Benzoyl-N-methylnitrosamine added to a stirred suspension of 2 eqs. ethyl mercaptan and 1.5 eqs. NaH in dry tetrahydrofuran at room temp, in the presence of 4A molecular sieves, and stirred for 20 min S-ethyl-thiobenzoate. Y 95%. F.e. inch S-aryl thiolates, also (more rapidly) from N-nitrocarboxylic acid amides, s. R. Beren-guer et al.. Synthesis 1989, 305-6. 

Nucleophilic replacement reactions (by AcS, Ph CO S , MeS , and PhCHaS") with methyl 0-toluene-p-sulphonyl-L-lactate and sodium L-2-chloropropionate give 2-acylthio- and 2-alkylthio-D-propionic acids and esters. Extensive racemization accompanies the use of excess thio-acetate or thiobenzoate, due to further 5 2 replacement reactions, as observed for LiAlH4 reduction of L-(2-methylthio)propionic acid or its methyl ester. Diborane reduction gives optically pure L-(2-methylthio)-propanol, however. This work includes a new synthesis of ( + )-2-mercaptopropionic acid, though by known methods, and establishes the D configuration for this isomer. 

Various routes to OO-diethyl dithiomalonate (202a) have been described, together with methods for its conversion into the analogous dithioester (202b) and bis-dithioester (202c). A simple procedure has been developed for the synthesis of unsymmetrical bis-acyl disulphides (203) from two thiobenzoic acids. ... 

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