Desulfurization of substituted

The phosphine-mediated desulfurization of substituted 1,2-dithianes to the corresponding tetrahydrothiophenes proceeds stereospecifically for the corresponding reactions of cis- and /ra r, 5-dihydroxy-l,2-dithianes 124 and 125/126, three different phosphines R3P (R=Et, Ph, (CH2)2COOH-HCl) were employed <2003H(60)47>. The reaction is pH-dependent under mildly acidic conditions, the thiols 127 and 128 were obtained under neutral or moderately basic conditions, however, the 4-hydroxy-3-mercaptotetrahydrothiophenes 129-131 were formed (Scheme 32). Erom 124 and 125 racemic 129 and 130 were obtained, while for 126 the stereospecific product 131 was isolated the identity of... 

A novel ring transformation/desulfurization of substituted 2-methyl-l,2,4-thiadiazolium salts 1481 provides a versatile entry to imidazoles 1482 with a variety of substituents. The starting 1,2,4-thiadiazolium salts 1481 can be prepared from A -(thiocarbonyl)-A -methylamidines 1480 under mild oxidative conditions. Related salts, 1,2,4-dithiazolium triiodides 1483, also react with amines to form imidazoles 1484 <1997JOC3480>. Alternatively, A -(thiocarbonyl)-A -methylamidines 1485 can be transformed into 1-substituted imidazoles 1487 via A-methylation followed by elimination of methylthiol (Scheme 383) <1997JOC3480>. 

Many other metals have been shown to be active in HDS catalysis, and a number of papers have been published on the study of periodic trends in activities for transition metal sulfides [15, 37-43]. Both pure metal sulfides and supported metal sulfides have been considered and experimental studies indicate that the HDS activities for the desulfurization of dibenzothiophene [37] or of thiophene [38, 39] are related to the position of the metal in the periodic table, as exemplified in Fig. 1.2 (a), 1.2 (b), and 1.2 (c). Although minor differences can be observed from one study to another, all of them agree in that second and third row metals display a characteristic volcano-type dependence of the activity on the periodic position, and they are considerably more active than their first row counterparts. Maximum activities were invariably found around Ru, Os, Rh, Ir, and this will be important when considering organometallic chemistry related to HDS, since a good proportion of that work has been concerned with Ru, Rh, and Ir complexes, which are therefore reasonable models in this sense however, Pt and Ni complexes have also been recently shown to promote the very mild stoichiometric activation and desulfurization of substituted dibenzothiophenes (See Chapter 4). 

The Gassman indole synthesis involves an one-pot process in which hypohalite, a P-carbonyl sulfide derivative 2, and a base are added sequentially to an aniline or a substituted aniline 1 to provide 3-thioalkoxyindoles 3. Raney nickel-mediated desulfurization of 3 then produces the parent indole... 

Another method of preparing ,to-diarylated alkanoic acids utilizes the condensation of 5-(w-phenylalkyl) substituted 2-thiophenealde-hydes (224) with benzyl cyanides and hydrolysis and desulfurization of the acids obtained (225). In this way, a,o-diphenylcaprylic acid has been prepared. ... 

Raney nickel desulfurization has been applied especially to the synthesis of different kinds of amino acids. a-Amino acids have been prepared by the Strecker synthesis of substituted thiophenealdehydes, followed by desulfurization of the thiophene a-amino acids. a-Amino-n-enantic acid, a-amino-n-caprylic acid, and norleucin have been obtained in about 50% yield from the appropriate thiophene aldehydes. From the desulfurization of thiophene -amino acids, obtained from the reaction of thiophenealdehydes with malonic acid in ammonia, aliphatic j8-amino acids, isolated as acetates, have been obtained in high yields. The desulfurization of 3-nitrothiophenes, such as (232), in ammonia leads to y-substituted amino acids (233). ... 

In the desulfurization of 3-substituted thiophenes several stereoisomers may be formed in certain cases. Both meso and racemic compounds have been obtained from the desulfurization of 3,4-diaryl-substituted thiophenes. It is claimed, however, that only meso, -diphenyladipic acid is obtained upon desulfurization of 3,4-di-phenyl-2,5-thiophenedicarboxylic acid and only di-isoleucin from 3-thienylglycine. The formation of small amounts of dimeric products in the desulfurization has been discussed with reference to the mechanism of this reaction. ... 

Both of the 4,5-tran.v-diaslereomers of 4,5-dihydro-4-(4-methoxyphenyl)-5-methyl-3-[(7 )-(4-methylphenylsulfinyl)methyl]isoxazole (24) show excellent stereoselection in reactions with aldehydes. Despite the bulky substituents at the 4,5-dihydroisoxazole nucleus, the stereochemical outcome of the reaction is controlled by the sulfoxide stereogenicity. The pairs of 4,5-dihydro-3-(2-hydroxyalkyl)-4-(4-methoxyphenyl)-5-methylisoxazoles, obtained by desulfurization of the corresponding aldol adducts, have the same configuration at the hydroxy-substituted carbon (C-2 ) and opposite configuration in the 4- and 5-positions of the dihydroisoxazole ring24. 

This preparation describes a convenient and general method of synthesis of substituted pyrimidines from compounds containing a /3-dicarbonyl group, either intact or as the corresponding ketal. The usefulness of the 2-mercaptopyrimidines is enhanced by the ease of removal of the mercapto group by desulfurization 9 or oxidation 10 and its replacement by other functional groups.1 ... 

A similar approach via desulfurization of the thiosemicarbazide-substituted pyrimidone 290 using 4-nitrobenzyl bromide leads to efficient formation of the tricyclic system 291 in excellent yield (Equation 79) <2000RJ0430>. 

In addition to DBT and BT, strain A11-2 could utilize methyl, dimethyl, and trimethyl DBTs as sulfur sources. The desulfurization of asymmetric alkylated DBTs was assessed to understand the sulfur specificity of this organism. It was shown to desulfurize several asymmetric alkyl DBTs up to C3-DBTs. It was shown that the rates of desulfurization depended on not only the position of alkyl substitution but also the number and length of alkyl substitution. An attempt was made to co-relate the data based on a molecular shape parameter. Selectivity of this organism was compared with R. erythropolis KA2-5-1 and, although clear differences were observed, the parameter fitting was not perfect. Two Paenibacillus strains, Paenibacillus sp. A11-1 and All-2, were patented [87] and were deposited as PERM BP-6025 and PERM BP-6026 in 1996 [122,123],... 

A class of enzymes capable of removing sulfur from alkane sulfonates exists, which may have relevance in microbial desulfurization of alkyl sulfides. A gene cluster ssuEADCB was identified in E. coli. The enzyme SsuD was capable of conversion of pentane sulfonic acid to pentaldehyde and sulfite. It was reported to be capable of conversion of alkyl sulfonates from C2 to CIO, as well as substituted ethanesulfonates and sulfonated buffers. The SsuE was a flavin-reducing enzyme that provided FMNH2 to the SsuD. 

Desulfurization of two LGO streams was studied using R. erythropolis rKA2-5-l [71] to determine the rate of desulfurization and develop a predictive model for desulfurization of diesel oil. The sulfur removal from various substituted DBTs was modeled using a competitive inhibition and lumping model and the desulfurization of the LGO streams was successfully assessed. The model consisted of a four component system based on... 

Desulfurization of highly substituted alkyl and aryl DBTs... 

A novel route to synthesize l,3 -triazine-2,4(l//,3//)-diones through the desulfurization of thiocarboamides, such as 1,3-disubstituted 2-thioureas, trisubstituted thioureas and N-substituted thioamides by silver cyanate has been reported <00H(53)929>. Treatment of urazole 23 with one equivalent of sodium hydride under anhydrous conditions, followed by addition of dimethyl sulfate, leads to l,3,5-triazine-2,4-dione 24 in 80% yield . 

In addition to the common methods of synthesis, it has been shown that the desulfurization of thioacetals yields organogermanes (Equations (7) and (8)) with excellent selectivity in some cases (Equation (9)).8 Ring-opening reactions of strained [l]ferrocenophanes furnish germanium-substituted ferrocenes9,10 (Equation (10)).9... 

Products isolated from the thermal fragmentation of A-arylbenzamide oximes and A-arylbenzamide O-phenylsulfonyl oximes have been accounted for by invoking a free-radical mechanism which is initiated by the preferential homolysis of the N-O bond." Time-resolved IR spectroscopy has revealed that photolysis of A, A -diphenyl-l,5-dihydroxy-9,10-anthraquinone diimine affords acridine-condensed aromatic products via excited-state intramolecular proton transfer." The absolute and relative rates of thermal rearrangements of substituted benzyl isocyanides have been measured,and it has been found that the relative rates are independent of temperature and exhibit excellent Hammett correlations. Thionitrosoarene (25), thought to be generated by desulfurization of the stable A-thiosulfinylaniline (24), has been established" " as an intermediate in the formation of 3,3a-dihydro-2,l-benzisothiazole (26) from o-alkylthionitrosoarene (24). 

Cyclic thiourea derivatives like l,3,4,5-tetramethylimidazole-2(3H)-thione— prepared by condensation of substituted thioureas with a-hydroxyketones—can be converted into the corresponding imidazolin-2-ylidene by desulfurization with sodium or potassium [Eq. (23)]. This method was used to prepare and isolate l,3-bis-neo-pentylbenzimidazolin-2-ylidene with Na/K. With LDA as the base it is also possible to generate free benzimidazolin-2-ylidenes in solution. ... 

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