Methylsulfanyl groups

The method has then been efficiently used to remove selectively the exocycHc methylsulfanyl group from phosphorylated thiopyranyl derivatives 85 resulting from hetero Diels-Alder reaction of a phosphono-dithioformate or dithioacetate (see Sects. 2.1.2 and 2.2.3). FimctionaHzed thiopyrans 86 [17,18,27a] are thus obtained (Scheme 25). Owing to this selective desulfanylation, phospho-nodithioesters can be used as heterodienophiles in place of the corresponding phosphonothioaldehyde, not described so far and probably very unstable. 

The guanidine moiety was incorporated by dimethyl (2,2,5,7,8-pentamethylchromane-6-sulfonyl N-alkylated amino) dithiocarbonate[264] (Pmc-dithiocarbonate) 91 in two steps. One methylsulfanyl group was replaced by the primary amino group of Bzl-Norn-OBzl in the presence of excess DIPEA and the isothiourea obtained was reacted with silver nitrate under basic conditions to yield the intermediate sulfonylcarbodiimide which reacts immediately with ammonia to yield the guanidine Bzl-Narg(Pmc)-OBzl 91. 

However, studies carried out with 5-valerolactone and organolithiums 496, 497 and 501 gave compounds 512-514, respectively715,716 (Scheme 135). Only intermediate 501 afforded the keto orthothioester without elimination of the methylsulfanyl group. 

Methylsulfanyl)purines are good starting materials for the preparation of aminopurines. This method can be successfully employed in the synthesis of 6-substituted aminopurines, e.g. 1, and 2, from 6-(methylsulfanyl)purine and 8-(alkylamino)-2-hydroxypurines from 2-hy-droxy-8-(methylsulfanyl)purine, but presents some difficulties when the methylsulfanyl group is in the 2-position. 

It was shown that the 2-methylsulfanyl group of 2-(methylsulfanyl)adenine could not be replaced successfully by ammonia under a variety of conditions and this experience was duplicated using allcylamines." However, in the case of 2-(methylsulfanyl)purin-6-ol it is possible to perform the displacement reaction in alcoholic amine solution to give, for example, the 2-dimethylamino derivative 3. ... 

The displacement of a methylsulfanyl group is facilitated when it is oxidized prior to the displacement reaction forming a sulfoxide or a sulfone as intermediate, e.g. formation of 8. ... 

Access to cyclopropanone thioacetals was provided by dibromocarbene addition to an alkene followed by sequential replacement of the bromine atoms with methylsulfanyl groups. Bi-cyclo[n.l. 0]alkanone thioacetals prepared in this way rearranged in the ring-enlargement mode when treated with formic or trifluoroacetic acid (Table 2). 

Upon the reaction of 1,2,3-tris(methylsulfanyl)cyclopropenylium ion 30 with pyrrole or indole compounds, the substitution of one methylsulfanyl group by the nitrogen-containing aromatic ring occurred to give the cyclopropenylium derivatives 31, which can be regarded as derivatives of protonated azacalicene. ... 

The other angular pyrazoloquinoline derivative 327 was obtained by hydrazinolysis of 2-imino-7,7-dimethy-4-methylsulfanyl-5-oxo-5,6,7,8-tetrahydro-2H-benzopyran-3-carbonitrile (326). The reaction can be proceeded by substitution of the methylsulfanyl group by hydrazine followed by cyclization to give 327 (97JCR(S)256) (Scheme 61). 

The sulfanyl substituents in 2-sulfanylpyrido[2,3-c/]pyrimidin-4-amine,79 2-sulfanylpyrido-[2,3-cf]pyrimidin-4(3//)-one,77 5,7-dimethyl-2-sulfanylpyrido[2,3-r7]pyrimidin-4(3//)-one,248 as well as methylsulfanyl groups in positions 2, 5, and 7 of pyrido[2,3-r/]pyrimidinones 226,316 have been removed by treatment with Raney nickel. 

Nucleophilic substitution of the methylsulfanyl group is also possible by treating 5-ethyl-3-(methylsulfanyl)-8-oxo-5,8-dihydropyrido[2,3-h]pyrazine-7-carboxylic acid (20) with amines such as pyrrolidine, dimethylamine, or ethylamine.62... 

The bromine atom in 2-bromopyrazino[2,3-6]pyrazines may be replaced by the methoxy or methylsulfanyl group under nucleophilic conditions.246 Unexpectedly, 6,7-dimethyl-2,3-bis(methylsulfanyl)pyrazino[2,3-h]pyrazine is formed (with introduction of a second methylsulfanyl group) when 2-bromo-6.7-dimethylpyra7ino[2,3-/>]pyrazine is treated with methanethi-ol in a solution of sodium methoxide in methanol at 201C for 4 hours [yield 19% mp 240-242 °C (cyclohexane)].246... 

Dithiazolium bromides 1 react with an excess of anhydrous ammonia at room temperature to give the amidinothioureas 2a, b (cf. Houben-Weyl, Vol. E8d, p 45ff), which undergo cyclization with thiophosgene in dichloromethane to afford the 2/f-1,3,5-thiadiazine-2-thiones 3a, b.105 Compounds 3a and b then react with iodomethane to yield the 1,3,5-thiadiazinium iodides 4 a and b.105 The methylsulfanyl groups of 4 a and b can be substituted by treatment with secondary amines to yield products 4c and d.105... 

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