Cyclizations sulfur compounds

Chloroacetone reacts with the hydrazinopyrimidine 508 to give the thienopyrimidotriazine 509 (Equation 233) <2000MOL835>, and cyclization of compound 510 to the thiazolopyrimidopyrimidine 511 is brought about by treatment with sulfuric acid (Equation 234) <2001IJB49>. 

The cyclization of certain 2-substituted isatin derivatives were studied so as to compare them with the above cyclizations. Thus, isatin- 2-thiosemicarbazone (126) and isatin-2-semicarbazone (127) underwent cyclization to 128 and 129 more easily than the corresponding cyclizations in the 3-series.406 As in the 3-series the sulfur compound underwent cyclization more easily than the oxygen.408 In contrast to... 

Reviews which cover heterocyclization of unsaturated sulfur compounds have been published recently.16 Cyclizations of sulfur systems can also be effected by radical chain mechanisms or by reactions in which the sulfur acts as an electrophile. Examples of nucleophilic sulfur functional groups used in heterocyclization reactions are shown in Figure 3. ... 

Cyclization of compound (74 R = H) in fuming sulfuric acid yielded the angular (75) and linear (76 R = H) products. Identity was confirmed by reductive dechlorination of the single product (76 R = Cl) obtained from compound (74 R = Cl) <82JHC1351>. 

Tetrahydrothiophenes are usually prepared by cyclizations resulting in the formation of a C-S bond or a new C-C bond in the -position to the sulfur atom . Two examples of such cyclizations are shown in Scheme 36. UV irradiation of chiral thiol 47 in the presence of AIBN affords tetrahydrothio-phene 48 without epimerization <20000L3757>. Intramolecular cyclization of compound 49 gives 2-cyanotetrahy-drothiophene 50 <1987S452>. 

OCTA and HeptaCTAs are formed, along with other polychlorinated aromatic sulfur compounds, as by products in the synthesis of pentachlorothiophenol from hexachlorobenzene. Pentachlorothiophenol is used as an additive for the improvement of the vulcanization process of rubber in the tire industry. The formation of OCTA is believed to occur by dimerization of pentachlorothio-phenate and by intramolecular cyclization and the formation of HeptaCTAs by dechlorination of higher chlorinated thianthrenes [27]. 

Cyclizations. A route to substituted naphthalenes by intramolecular cyclization involves attack by a nascent allyl anion to a ketone group. On the other hand, the generation of N-arylindolines from arylamines and o-halostyrenes is a more complex process. Arylamines. The Pd-catalyzed arylation of amines depends critically on l-BuOK. Synthesis of sulfur compounds. a-Sulfenylation under mild conditions is realized... 

Cyclization of compounds such as a-benzyl-a-allylacetic acid by moderate heating in concentrated sulfuric acid to yield tetralin derivatives. 

Heteroaromatic amines react with alkylpyridines in the presence of sulfur to give the corresponding thioamides. For example, from 3-aminopyridazine, with 2-methylpyridine and sulfur, compound 219 is obtained. When, however, the 2-methylpyridine (or diethyl malonate) was used in catalytic amount, 3-aminopyridazine-5(2H)-thione (220) was obtained at 160°-170°C.474 Pyridazine-3-thiones react with a-halocarbonyl compounds to give the corresponding keto-sulfides, which can be further cyclized.475... 

In 1982, Ueno reported the first uses of allylic sulfur compounds for carrying out the allylation of a carbon-centered radical [48], The reactions detailed are cycliza-tion reactions in which an aryl radical adds to an allylic sulfide to form either an indole or benzofuran product (Scheme 17). Tin, in the form of tributyltin hydride, was used to carry the radical chain. With low concentrations of tin hydride, yields of the desired products as high as 96% were observed. A more recent set of examples of cyclizations onto allylic sulfides was reported by Ward in 1991 [49]. 

The -fragmentation can be used as one of the cascade steps in processes which do not start from the addition of a sulfur-centered radical. Rearrangements of sulfur compounds, catalyzed by tributylstannyl radical, which lead to 3-vinyldihydrothiophene or dihydrothiopyran derivatives, have been developed [70]. The mechanism is shown in Scheme 15 the cyclic y9-thioalkyl radical 9, produced in two steps, fragments, thus producing the thiyl radical 10, which cyclizes in a 5- or 6-endo fashion onto the stannylated double bond subsequent elimination leads to the final heterocyclic compound. 

Oxidative heterocyclization. Sulfur compounds undergo oxidation, and when the Ulfur atom is separated from a polymethoxylated aromatic nucleus by three, four, or five bonds, cyclization ensues (8 examples, 53-98%). 

Properties and Reactions of Ylidenemalononitriles, F. Freeman (1980). Dicyanomethylene compounds, their molecular structure and spectral properties, toxicity and analyses are reviewed. Various reactions like hydrolysis, oxidation and reduction, dimerizations, cyclizations, photochemistry and thermolysis are discussed. The review, which contains 380 references, also deals with unsaturated compounds, oxygen, nitrogen, phosphorous and sulfur compounds. 

Their substrates are 2-phenylpyridines, imines, benzo[/i]quinones, phosphines, oxygen compounds, sulfur compounds, etc., as described in the previous sections or in Fig. 5.11, Tables 5.5 and 5.6. These reactions are arylations, alkenylations, alkylations, acylations, cyclizations, hydrogenations, oxidations, hydrosilylations, dehydrogenations, etc. 

Adding PEEK and PAI for electro-technical applications, where gas released from PPS plays a role, the upper service temperature of PPS can be increased by 20 to 50 K. With polymer additives, such as polyvinyl carbazole that exhibit lower heat resistance than PPS, their long-term effect is questionable, because these additives slowly degrade [573]. The active mechanisms for this behavior have not yet been explained. Pure absorption in the form of addition complexes must be excluded because of the effectiveness at high temperatures. More probable is the integration of sulfur compounds in the chain of the additive polymers, possibly with further cyclizations [573]. 

The effect on the Bergman cycloaromatization of sulfur-containing substituents in the acetylene branch was studied for simple models, such as butyl-2-(triisopropylsilylethynyl)phenylethynylsulfide 3.922 (Scheme 3.133) [411]. The starting sulfide 3.922 was synthesized by treatment of the mono-trisopropylsilyl-protected orf o-diethynylbenzene 3.921 with butyllithium excess followed by the addition of sulfur dichloride [411]. Cyclization of compound 3.922 (benzene, 200°C, 6 M of 1,4-cyclohexadiene) gave butyl-2-naphthylsulfide 3.923 in 53% yield. Comparison of the parameters of this reaction with the cyclization of ortho-diethynylbenzene showed that the presence of the sulfur atom increases the cyclization barrier although the yield from compound 3.922 is much less than that from ort/ o-diethynylbenzene. These studies are consistent... 

The cyclization of 5-(2-carboxyanilino)pyrimidine (170) with sulfuric acid/phosphoric acid leads to the 7-chloropyrimido[5,4-A]quinolinetriones (171) (57JCS4997, 74KGS131), the 2,4,10-trichloro compounds being obtained with phosphoryl chloride (72JHC91), whilst a formally similar cyclization of 4(6)-arylamino-5-ethoxycarbonylpyrimidines gives... 

The intermediacy of an aci-nitro compound has been proposed for the sulfuric acid cyclization of o-nitrophenylacetic acid to yield a mixture of 2,1-benzisoxazole and 2,1-benzisoxazole-3-carboxylic acid. The acid does not decarboxylate under the reaction conditions. The proposed aci-nitro intermediate cyclized to an A/ -hydroxy compound which decomposed to the products (Scheme 179) (70JCS(C)2660). 

Benzisothiazoles are best prepared by oxidative cyclization of o-aminothiobenz-amides (see Section 4.17.9.1.1), reaction of o-toluidines with thionyl chloride (see Section 4.17.9.2.1) or by sulfuration of 2,1-benzisoxazoles (see Section 4.17.10.2). 1,2-Benzisothiazoles can also be prepared from o-disubstituted benzene compounds, cyclodehydration of o-mercaptobenzaldoximes or oxidative cyclization of p-mercaptobenzylamines (see Section 4.17.9.1.1) being the most convenient. Both series of benzo compounds are readily substituted at the 5- and 7-positions by electrophilic reagents. 

Cyclization of the diazo compound (108) with a copper catalyst affords the clavulanic acid derivatives (110) and (111), possibly via rearrangement of the sulfur ylide (109) (80H(14)1999). Similar reactions have been reported in the recent literature (80H(14)1967, 81H(16)1305, 80TL31). 

Shortly after their first report of all-oxygen bridged cryptands, Dietrich, Lehn and Sauvage reported incorporation of sulfur in the strands. The experimental methods used were essentially similar to those applied in the syntheses of the parent cryptands. As in previous cases, a diacyl chloride was condensed with a diamine under high dilution conditions. In this case, however, the diamine contained sulfur atoms rather than oxygen. The synthesis of compound 5 was accomplished in two stages as illustrated below in Eq. (8.3). The first cyclization step affords the macrocyclic amine in 55% yield. The macrobicyclic product (5) is formed in 25% yield from the monocyclic diamine and the acid chloride. 

In addition there are certain other methods for the preparation such compounds. Upon heating of the thionocarbonate 2 with a trivalent phosphorus compound e.g. trimethyl phosphite, a -elimination reaction takes place to yield the olefin 3. A nucleophilic addition of the phosphorus to sulfur leads to the zwitterionic species 6, which is likely to react to the phosphorus ylide 7 via cyclization and subsequent desulfurization. An alternative pathway for the formation of 7 via a 2-carbena-l,3-dioxolane 8 has been formulated. From the ylide 7 the olefin 3 is formed stereospecifically by a concerted 1,3-dipolar cycloreversion (see 1,3-dipolar cycloaddition), together with the unstable phosphorus compound 9, which decomposes into carbon dioxide and R3P. The latter is finally obtained as R3PS ... 

Ullmann condensation of the sodium salt of p-chlorothiophe-nol (31) with 2-iodobenzoic (32) acid gives 33. Cyclization by means of sulfuric acid affords the thioxanthone, 34. Reaction with the Grignard reagent from 3-dimethylaminopropyl chloride affords the tertiary carbinol (35). Dehydration by means of acetic anhydride affords chlorprothixene as a mixture of geometric isomers, 36. (Subsequent work showed the Z isomer-chlorine and amine on the same side—to be the more potent compound.) Chlorprothixene is said to cause less sedation than the phenothiazines. ... 

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