N- and S-Heterocycles

Wittig reactions have also been employed in domino processes. For example, Schobert and coworkers developed an effective addition/Wittig reaction protocol which provides access to a, 3-disubstituted tetronic acids, tetronates, as well as to five-, six- and seven-membered O-, N-, and S-heterocycles [149]. 

Many desirable meat flavor volatiles are synthesized by heating water-soluble precursors such as amino acids and carbohydrates. These latter constituents interact to form intermediates which are converted to meat flavor compounds by oxidation, decarboxylation, condensation and cyclization. 0-, N-, and S-heterocyclics including furans, furanones, pyrazines, thiophenes, thiazoles, thiazolines and cyclic polysulfides contribute significantly to the overall desirable aroma impression of meat. The Maillard reaction, including formation of Strecker aldehydes, hydrogen sulfide and ammonia, is important in the mechanism of formation of these compounds. 

Five- to seven-membered O-, N-, and S-heterocycles Acyl ylides with a tethered terminal ester function requisite for the construction of five- to seven-membered heterocycles are very conveniently accessible by reaction of the cumulated ylide ketenylidenetriphenylphosphorane 11 with various carboxylic esters bearing OH-, NHR-, and SH-groups in a-, -, or y-position. 

Electron-nuclear double resonance spectroscopy of metalloenzymes with N- and S-heterocycles as ligands 03ACR522. 

Synthesis of P-nitroamines via Mannich and aza-Henry reactions including the synthesis ofnitro N- and S-heterocycles 13COC1200. Synthesis of heteroaromatic compounds by newly extended Pummerer reactions 13YGK341. 

Five-membered heterocycles with N and S (Se) atoms 97PF1C190,98PF1C172, 99PHC184. 

Eormation of N-, 0-, and S-heterocycles in reactions with participation of hy-pervalent iodine (25 years of development at University of Thessaloniki) 98SL221. 

Amfidinolides (unique macrolides from marine dinoflagellates) 97H(44)543. Antitumor N-, N,S-, and S-heterocycles and macrocyclic lactams from ascidi-ans 97M122. 

Conformational flexibility of six-member dihydro N-, O- and S-heterocycles 97IZV2095. 

Cao and coworkers synthesized three series of copolymers 348 [426], 349 [427], 350 [428], and 351 [429], exploiting random copolymerization of fluorene fragments with dibromo-derivatives of Se,N and S,N heterocycles (Scheme 2.55). Fluorene-benzoselenadiazole... 

Abstract The development of a new method for the regioselective synthesis of functionalized indoles and six-membered benzo-fused N-, O-, and S-heterocycles is reported. The key step involves the generation of a benzyne-tethered vinyl or... 

As rich and varied as the chemistry of boron-carbon heterocycles is, its versatility is extended considerably by the introduction of additional elements as ring heteroatoms (T able 6). At this writing, development in this area has involved primarily N- and S-containing rings, but examples of P- and O-containing boron heterocycles are also known. 

Heterocyclic These are compounds having at least one hetero atom (any other atom but carbon, e.g. O, N and S) within the ring, and conforming to Hiickel s rule. The aromaticity of heterocyclic compounds, e.g. pyridine and pyrrole, can be explained as follows. 

Studies on the Chemistry of Thienoannulated 0,N- and S,N-Containing Heterocycles. 1. Nucleophilic Substitution Reactions on Chlorinated Thiophene Derivatives as a Basis for the Synthesis of Thienoannulated 0,N- and S,N-Heterocycles, Puschmann, I. Erker, T. Heterocycles 1993,36,1323. See also Studies on the Chemistry of Thienoanellated 0,N- and S,N-Containing Heterocycles. II. Synthesis on Thieno-Dilthiazem Analogs, Puschmann, 1. Erker, T. Heterocycles 1995, 41, 709. 

N-, 0-, and S-heterocyclic ligands also form [Os(NH3)5 t)2-(C,C)-L ]2+ complexes [L = 2,6-lutidine, 2,6-lutidinium, pyridinium, N-methylpyridinium, and lV-methyl-4-picolinium (85, 167), NJV -dimethylimidazolium (90), pyrrole (90, 179), IV-methylpyrrole (90, 179), thiophene (90,179), furan (90,179), and 1,3-dimethyluracil (72, 73)]. On oxidation to Os(III), arene ligands are rapidly lost from the coordination sphere, or in the case of the substituted arene ligands with good a donors, rapid linkage isomerization reactions occur (Section V,D). 

Heterocyclic compounds contribute significantly to the overall aroma impression of meat. They include 0-, N-, and S-hetero-cyclic structures. Meat flavor heterocyclics include furans,... 

The methyl group on SAM behaves as an electrophilic +CII3 positively charged carbocation that is attracted to electron-rich nucleophilic O, N, and S atoms on a xenobiotic compound methylation of carbon is rare. Therefore, the kinds of compounds commonly methylated include amines, heterocyclic nitrogen compounds, phenols, and compounds containing the -SH group. A typical methylation reaction is that of nicotine ... 

N,S- and N,0,S-Heterocycles as precursors of N2S, thiofulminic acid, and nitrile sulfides 91CRV363. 

Scrutiny of a number of other five-membered C-, N- and S-containing heterocycles (78JCS(P1)1445) with the framework depicted in Scheme 2 has revealed that facile photofragmentation takes place when extrusion of a small inorganic fragment such as N2 (thiatriazole), N20 (thiatriazole 3-oxide), CO, C02, etc. is possible. In these cases formation of nitrile... 

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