Thiocarbonyl sulfur

Step 2 On reaction with hydrogen chloride m an anhydrous solvent the thiocarbonyl sulfur of the PTC derivative attacks the carbonyl carbon of the N terminal ammo acid The N terminal ammo acid is cleaved as a thiazolone derivative from the remainder of the peptide... 

Other side reactions that have been reported are cleavage of the carbon-nitrogen bond to form 24 and an aminyl radical 25 or scission of the tliiocarbonyl-sulfur bond to form a thiyl radical 26 and 27 (Scheme 9.I0). U 6 4 Thiocarbonyl-sulfur bond cleavage may be a preferred pathway in the case of primary dithioearbamates. 

An extensive series of thiosemicarbazones obtained from 2-acetylpyridine was tested by Klayman et al. [4, 85] for antimalarial activity against Plasmodium berghei in mice. The molecular features essential for activity were found to be a 2-pyridylethylidene moiety, the presence of the thiocarbonyl sulfur, and certain, bulky or cyclic substituents at the terminal AT-atom. The most active 2-acetylpyridine thiosemicarbazones were " N-phenyl- and those with azacycUc substituents. For example, iV-substituents of 4-methylpiperidine, piperazine, and azabicyclo[3.2.2.]nonyl-, 4, were curative at a dose level as low as 20 mg/kg. 

One of the most important parameters to determine the reactivity is the distance between the thiocarbonyl sulfur (S) and the alkenyl carbon atom (C6) in Table 1, because a new bond will be formed between these two atoms at the initial step of the photoprocess. The actual distance of the (Z,E)-conformation imide la is 3.59 A, which is closely placed and is almost the same as the sum of the van der Waals radii 3.50 A. In the (EyE) conformation, the atomic distances are longer than that of la, and are 4.13 A for Ic and 4.32 A for Id. For the second step of cyclization, the atomic distance between the thiocarbonyl carbon (C2) and the alkenyl carbon (C5) is in the range from 3.00 to 3.11 A, which is much smaller than the sum of the van der Waals radii 3.40 A. From this geometrical consideration of the site of the new bond formation, it is expected that the reaction leading to thietane will smoothly progress. 

From the X-ray structural analysis of the starting thionocarbamate 3b, the distance between the thiocarbonyl sulfur atom and the alkenyl carbon and between the thiocarbonyl carbon and the alkenyl carbon is 4.69 and 3.00 A, respectively. The fact that the reaction proceeded under these restricted conditions, in which the distance of each reacting site is longer than the sum of the van der Waals radii (3.5 A), is accounted for by the fact that the initial reaction occurred in the defect of the crystalline lattice, with the later reaction occurring in increasingly defective regions. Furthermore, two plausible factors are responsible for the relatively low enantiomeric excess of 3b. 

Sakamoto et al. provided the first example of hydrogen abstraction by thiocarbonyl sulfur in the solid state [37,38]. Irradiation of AT-diphenylacetyl-AT-iso-propylthioaroylamides 6 in the solid state gave thioketones 7 (P-hydrogen abstraction products by thiocarbonyl sulfur), mercaptoazetidin-2-ones (y-hy-drogen abstraction products by thiocarbonyl sulfur), and aroylthioamides (y-hydrogen abstraction products by thiocarbonyl sulfur followed by cleavage). 

Alkylation of the thiocarbonyl sulfur of thiosemicarbazone derivatives induces not only complexation through the terminal amino group but also enough acidic character for it to... 

The reaction of alkyl isothiocyanates, RNCS, with diphenylphosphinic hydrazide (338) in benzene has been reported.308 The bis(diethylamino)[(methylthio)thiocarbon-yl]carbenium salts (339 X = I or BF4) display ambident reactivity and can react either at carbenium carbon (hard nucleophiles) or at the thiocarbonyl sulfur atom (soft nucleophiles).309 Electrochemically generated superoxide reacts with dithioic S,S -diesters (dicarbothiolates) (340 Ar = C5H3N or C6H4) to give the monocarboxylate anions in 100% yield before giving the dicarboxylate anions.310... 

Due to the highly nucleophilic and polarizable thiocarbonyl sulfur, thioketones react with a large variety of electrophiles E+. In the case of thioaldehydes and thioketenes this... 

Organometallic thioketones behave as dienophiles in the reactions with cyclopenta-diene497 and also undergo attack by butyllithium to give mostly reaction at the thiocarbonyl sulfur. The organometallic moiety (ferrocenyl, Mn complex etc.) is inert under these reaction conditions498. 

Sakamoto et al. provided an example of absolute asymmetric synthesis involving hydrogen abstraction by thiocarbonyl sulfur (Scheme 6). [24] Achiral A -diphenylacetyl-iV-isopropylthiobenzamide 33 and Y-diphenylacetyl-A-isopropyl(p-chloro)thio-benzamide 33 crystallize in chiral space group P2 2 2. Photolysis of the chiral crystals in the solid state gave optically active azetidin-2-ones whereas achiral thioketones were obtained as main products. When 33a was irradiated in the solid state at -45°C followed by acetylation (at -78°C), 2-acetylthio-3,3-dimethyl-l-diphenylacetyl-2-phenylaziridine (34a 39% yield, 84% ee), 4-acetylthio-5,5-dimethyl-2-diphenylmetyl-4-phenyloxazoline (35a 10% yield, 50% ee), 3,3-diphenyl-1-isopropy 1-4-... 

Eq. 3.7 shows the cyclization of the xanthate ester (20) formed from homopropargyl alcohol, through 5-exo-dig manner of the formed carbon-centered radical. This reaction is not a deoxygenation reaction of alcohol, but the cyclization of the carbon-centered radical formed from the addition of Bu3Sn to the thiocarbonyl-sulfur atom, onto the side-chained triple bond to form thionolactone, the hydrolysis of which readily creates lactone (21) [21-23]. 

Eq. 3.20 shows the addition of Bu3Sn to thiocarbonyl sulfur of compound (61) to form carbon-centered radical, which cyclizes to olefinic group via 5-exo-trig manner to give thiollactone (62), after hydrolysis. 

R group in front of the thiocarbonyl sulfur atom. The experimental barriers were constant in the series R = Me, Et, iPr. This abnormal behavior was accounted for by considering the increase in strain in the ground state as was shown by molecular mechanics calculations (80OMR166). The barrier to rotation of the neopentyl group was determined in anhydro-2-methylthio-3-neopentyl-4-hydroxy-5-phenylthiazoline hydroxide (AG = 45kJmol 1) (86ACS(B)751). Many other heteroaromatic series are suitable for such studies. 

Scheme 13 Asymmetric synthesis using hydrogen abstraction by thiocarbonyl sulfur.

Two methods have been utilized for the preparation of 0-[(alkylthio)car-bonyl] derivatives (X—0—CO—S—R). The thiocarbonyl sulfur of an 0-[(alkylthio)thiocarbonyl] compound has been specifically oxidized by silver nitrate. However, the action of (S-alkyl thiochloroformates upon a... 

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