Formation of S-Heterocycles

In the field of constructing S-heterocycles, a reaction involving a low loading of Takemoto s catalyst 3 was used in the synthesis of succinimide-containing 

The process of enamine formation/aldol condensation/Michael addition/6-exo-trig cychzation/elimination cychzation was used to prepare thienothiopyrans. As 

2- [(2-ethoxy-2-oxoethyl)sulfonyl]acetate, aromatic aldehydes, and 5-aryltetrahydro- 

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Formation of S-heterocycles on reactions of CS2 with C-nucleophiles 91MI52. 

Formation of S-heterocycles mediated by sulfonate- and sulfonamide-stabilized carbanions 03EJO3713. 

Divinyl sulfides, formation of S-heterocycles from 84SR(3)323. Electroreduction in synthesis of N,S-heterocycles 85YGK496. 

Blechert s synthesis of the piperidine alkaloid (-)-halosaline (387) by Ru-catalyzed RRM is outlined in Scheme 76 [160]. In the presence of 5 mol% of catalyst A, the ring rearrangement of metathesis precursor 385 proceeded cleanly with formation of both heterocyclic rings in 386. In situ deprotection of the cyclic silyl ether in 386, followed by selective reduction and removal of the to-syl group led to 387. 

In addition to his total synthesis of pamamycin-607 (lb) (see Schemes 14-17), Kang also communicated an alternative synthesis of a larger fragment surrogate of lb [51]. Again, iodoetherifications of y-triethylsilyloxy alkenes were utilized as key transformations to control the 2,5-c/s-disubstitution of the two tetrahydrofuran moieties. However, whereas his total synthesis of lb involved a two-directional formation of both heterocycles in a single operation, the alternative route depicted in Schemes 31 and 32 is characterized by sequential... 

The formation of oxygen heterocycles through carbon-oxygen bond formation was also reported. Substituted 2-(o-halophenyl)-ethanols were converted to dihydrobenzofuranes using palladium and Buchwald s bulky biaryl-type ligands (3.43.). The reaction was also efficient in the formation of six and seven membered oxygen heterocycles.53... 

Mottram, D.S. 1985. The effect of cooking conditions on the formation of volatile heterocyclic compounds in pork. J. Sci. Food Agric. 36 377-382. 

Nucleophilic attack at ring sulfurs can proceed at S-l as well as S-2 atoms. The cleavage of the S-S bond in the 1,2,3-dithiazole ring and formation of sulfur heterocycles in the first case, or the formation of compounds with C=S group by the attack on S-2 atom, are the results of these reactions. 

F. B. Whitfield, D. S. Mottram, S. Brock, D. J. Puckey, and L. J. Salter, Effect of phospholipid on the formation of volatile heterocyclic compounds in heated aqueous solutions of amino acids and ribose, J. Sci. Food Agric., 1988, 42, 261-272. 

S. Zochling, and M. Murkovic, Formation of the heterocyclic aromatic amine PhIP Idenfication of precursors and intermediates, Food Chem., 2002, 79, 125-134. 

Terminal perfluoroolefins have two fluorine atoms at the double bond. The carbon atoms of the latter bear a significant positive charge, and the nucleophilic agents easily replace the fluorine atoms at the multiple bond. The reactions of binucleophilic reagents with terminal perfluoroolefins form heterocyclic systems. The first step of the reaction involves a nucleophilic attack at the carbon atom of the double bond, generating a carbanion. The latter is stabilized by elimination of the fluoride ion and formation of a new double bond. Subsequent cyclization by the intramolecular attack of the nucleophilic center at the double bond leads to the formation of a heterocyclic system. For example, when a reaction mixture of hexafluoropropylene and sodium dialkylaminodithiocarbamate in dimethylacetamide is heated with aqueous sodium tetraphenylborate, one obtains the tetraphenylborate salt of 2-dialkylamino-4-trifluoromethyl-4,5-difluoro-l,3-dithiolan-2-yl (78JFC(12)193). This compound is formed by intramolecular cyclization of the S-nucleophilic center. 

If other active groups are present y or S to the reducible nitro group, hydrogenation can result in formation of nitrogen heterocyclic products. Several such cyclizations provide an entry to indoles, such as reductive cyclizations of dinitrostyrene 1 [equation (a)], of o-nitrobenzyl ketone 2 [equation (b)], and of nitro nitrile 3 [equation (c)] , all of them carried out on palladium-on-carbon. 

The 5,6-dihydro-477-l,2,6-thiadiazine 1,1,2-trioxides (162) described in Section 6.16.9.2.3.1 are susceptible to nucleophilic attack at sulfur, which promotes heterolytic cleavage of the heterocyclic ring and formation of )S-hydroxyaminosulfamic acid derivatives (163) as outlined in Scheme 15 <90LA775>. However, with a primary amine as the attacking nucleophile the sulfamides (163) so formed undergo base-catalysed ring closure to the 4,5-dihydropyrazoles (164) in yields of 72-90%. 

Dehydration o1 primary nitro compounds (Mukeuyama reaction) affords nitrile oxides, which may dimerize to yield furoxans, or otherwise be trapped by suitable dipoiatophiles such as double or triple bond systems, leading to the formation of various heterocyclic systems, S. The latter have been used for further derivatization in the heterocyclic series, or in return as precursors of acyclic products after ring cleavage, for example, 1,3-amino alcohols 6 or p-hydroxycarbonyl compounds, 9. 

The five-membered ring products result from the normal (Markownikoff) internal addition of the thiol group to the double bond, whereas the six-membered ring products result from abnormal (anti-Markownikoff) addition, which is characteristic of a free radical process. The formation of both heterocycles thus indicates competitive thermally induced heterolytic and homolytic fissions of the thiol S—H bond (equation 7). The cyclization mechanisms were verified by a detailed examination of the thermal behaviour of 104. Product 102 was formed almost exclusively... 

Methylation of -OH, -SH, -NHg and -NH groups occurs widely among species. Methylation of heterocyclic nitrogen compounds occurs in mammals, birds, frogs, turtles, and some insects. Methylation of phenols occurs in mammals, molds, and plants [20]. An enzyme in the soluble fraction of many tissues catalyzes the formation of S-adenosylmethionine. The active methyl group of S-adenosylmethionine is then transferred to various acceptors by a variety of transferases. 

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