Thioamide chiral

A variety of nucleophiles can be employed—e.g. carboxylic acids, phenols, imides, thiols, thioamides, and even /3-ketoesters as carbon nucleophiles. Of major importance however is the esterification as outlined above, and its use for the clean inversion of configuration of a chiral alcohol. 

Yan s group has used the camphor-based chiral thioamide 62 in asymmetric Darzens reactions (Scheme 1.21) [32]. The addition of the titanium enolate of 62 to... 

An asymmetric synthesis of phosphonylated thiazolines has been described. The phosphonodithioacetate 46 was aminated with a chiral amino alcohol 47 to give the phosphonylated thioamide 48 in good yield. This was then cyclised using a Mitsunobu procedure to give the chiral thiazoline phosphonate 49 in good yields under mild conditions. Homer-Wadsworth-Emmons reaction of these phosphonylated thiazolines gave chiral vinylic thiazolines 50 <00S1143>. 

X-ray crystallographic analysis also revealed that the crystal of thioamide la was chiral, the space group P2i2i2i. The absolute configuration of (-)-rotatory crystals of la, where the optical rotation was assigned on the basis of CD spectra in a KBr pellet, was determined by the X-ray anomalous scattering method as (-)-(M)-la for the helicity. When (-)-rotatory crystals were irradiated at 0 °C until the reaction conversion reached 100% yield, the asymmetric induction in... 

X-ray crystallographic analysis revealed that the crystals of thioamide 24b are chiral and the space group was P2i2i2i. When the crystals were irradiated... 

In the solid-state photochemical reaction of N,N-disubstituted a,(3-unsatu-rated thioamides 24, a crystal-to-crystal nature was observed in 24c furthermore, absolute asymmetric transformation in the chiral crystalline environment was performed in the photoreaction of 24b, 24c, and 24e. 

X-ray crystallographic analysis also revealed that the crystal of thioamide la was chiral, the space group The absolute configuration of (-)-rotatory... 

C-Terminal activation of peptides containing a terminal thioamide group results in thiazo-lone formation this leads to epimerization at the marked chiral centers (see Scheme 35) the thiazolone is only a weak acylating agent 500 The coupling yield may still be satisfactory, if achiral C-terminal amino acids are employed 488,503 ... 

Various more or less efficient methods have been reported for the synthesis of 2-(l-ami-noalkyl)thiazole-4-carboxylic acids and their suitably protected derivatives. 237,539,541,558-568 Optimal conditions must be selected in these syntheses to prevent racemization at the chiral aminoalkyl moiety, e.g. when applying a modified Hantzsch synthesis 559 racemization has been observed to occur at the level of the starting Na-protected amino acid thioamide as well as in the base-mediated dehydration step of the intermediate hydroxydihydrothiazoles. 558 The 2-(aminoalkyl)thiazole-4-carboxylic acids are incorporated into the linear precursors by standard procedures of peptide synthesis, 237,514,529,539,552,555,558,564,569 and cyclization is pref-... 

The thioamide 44 was prepared in 78% yield from the treatment of Boc-D-Val-NH2 (43) with Lawesson s reagent in CH2C12. Thioamide 44 was then treated with KHCO3 and ethyl bromopyruvate from -40 °C to -20 °C in order to form the intermediate hydroxy-dihy-drothiazole 45 (not isolated) which was subsequently dehydrated with (Tfa)20 and 2,6-lutidine at -20 °C to form the dipeptide thiazole 46 in 73% yield based on thioamide. The product was ascertained to be essentially one enantiomer (>99% ee by chiral HPLC). 

The solid-state photoreaction of thioamide 1 was done under an atmosphere purged with dry argon. The solid sample was irradiated for 4 h as a powder prepared by grinding, and placed inside a Pyrex slide. When powdered thioamide 1 was irradiated in the solid state at 0 °C, at up to 19% conversion, optically active /i-thiolactam 2 of 31% ee was isolated. The optical purity was determined by HPLC using a chiral cell OD column (Daicel Chemical Ind.). 

L-Prolinethioamides (39, R = alkyl including chiral alkyl), prepared from proline and amines, are effective in acetone-benzaldehyde reactions.110 Mechanistic studies focused in particular on suppression of non-enantioselective side-reactions, and also on the role of the side-chain of the catalyst acting as hydrogen bond donor, especially as the thioamides (with their more acidic N—H protons) are more catalytic than their amide analogues. 

Enantioselectivity of the photochemical conversion of the thioamide 25 in its chiral crystals into 26 (96% yield at 58% conversion, 81-97% ee) is quite high, as indicated [18]. 

The aldol reaction of dithioester enethiolates has been used for the synthesis of dithiolactones [123], chiral substrates for the Claisen rearrangement [124, 125], and oxathianes [126]. Thioamide enethiolates may be employed in this reaction as well as shown with /Tthiolactams [26], or with a precursor of the antitumour agent vinblastine [127]. 

X-ray crystallographic analysis revealed that the crystals of thioamide 32b are chiral and the space group is P2 L lx. Dextrorotatory crystals were irradiated at 0°C until the reaction conversion reached 81 % yield. As expected, the asymmetric induction was observed, and optically active 33b (55% ee) was isolated (Table 5). As a consequence of the suppression of the reaction conversion yield from 81% to 17%, the enantiomeric purity rose up to 74% ee. p-Thiolactam 33b with only Z-configuration was isolated, and the absolute configuration of ( + )-33b was determined as (3S,4S)-isomer by the x ray anomalous scattering method. 

Chiral dialkyl tartrate-diethylzinc complexes catalyze the asymmetric ring opening of symmetrical AT-acylaziridines (e.g., 76) with thiols to give thioamides (e.g., 78) with up to 93% ee. The enantioselectivity is dependent upon the stoichiometry of the reactants and the nature of the tartrate (Scheme 21) <1996T7817>. 

This protocol has been successfully applied to the reactions of carboxylic acid derivatives such as thioamides and thione esters (cqs 3 and 4). 3-Acetylthiazolidine-2-thiones are quite suitable substrates for the tin(ll) enolate mediated asymmetric aldol reaction and various optically active p-hydroxy 3-acetylthiazolidine-2-thiones are obtained by using chiral diamine 1 (eq 5). ... 

Achiral thioamide (412) crystallises in a chiral space group and irradiation of the powdered crystals leads to exclusive formation of optically active p-thio-lactam (413) with high enantiomeric excess by a mechanism involving intramolecular transfer of the appropriately-oriented benzylic hydrogen and cyclisation with minimal molecular motion within the crystal. S-(o-Tolyl)-o-benzoylbenzo-thioate also crystallises in a chiral space group. Irradiation of a solid sample of a single enantiomorphic modification yields optically active 3-phenyl-3-(o-tolyl-... 

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