Sulfur atom of the

The sulfur atom of the thiocarbonyl group is a good nucleophile, and reaction between benzyl bromide and l-(2-thiazolyl)thiourea yields the isothiouronium salt (496). The sulfur atom may also be engaged in a chelate, as exemplified by the Cu chelate of 2-thioureido-4-methylthiazole (491). These chelates with metal ions were thoroughly studied in acidic, neutral, and alkaline media for 66 metal ions in order to define their analytical use. They are formed in the molar ratio of 1 2 for metal II compounds (498). 

A major advance was devised by Pehr Edman (University of Lund Sweden) that has become the standard method for N terminal residue analysis The Edman degrada tion IS based on the chemistry shown m Figure 27 12 A peptide reacts with phenyl iso thiocyanate to give a phenylthwcarbamoyl (PTC) denvative as shown m the first step This PTC derivative is then treated with an acid m an anhydrous medium (Edman used mtromethane saturated with hydrogen chloride) to cleave the amide bond between the N terminal ammo acid and the remainder of the peptide No other peptide bonds are cleaved m this step as amide bond hydrolysis requires water When the PTC derivative IS treated with acid m an anhydrous medium the sulfur atom of the C=S unit acts as... 

The formation of diazosulfones and diazosulfonates can also be described as S-coupling. Here the sulfur atom of the sulfinic acid or the sulfite ion, respectively, appears as the basic centre of the nucleophilic component, whereas the oxygen atoms do... 

A remarkable case of a Meerwein reaction of phenylacetylene was reported by Leardini et al. (1985) in a new synthetic route to benzothiophene derivatives. Aryldi-azonium salts with a thioether group in the 2-position add phenylacetylene and substituted phenylacetylenes in the presence of metallic copper or iodide ion in acetone, or of FeS04 in DMSO (Scheme 10-60). The radical 10.21 formed initially is attacked intramolecularly by the sulfur atom of the thioether group to give the benzothiophene 10.22 in high yields (55-95%) as shown in (Scheme 10-60). Lear-... 

The nucleophilic attack of strong bases (e.g. hydroxide ion, alkoxide ions and carbanions) on either the a-carbon111 or the sulfur atom of the sulfone group99,113 of the thiirane dioxides is the initial key step that is responsible for the subsequent ring opening and further reaction. The formation of a three-membered a-sulfonyl carbanion is not observed in these cases (equation 11). 

A direct attack of nucleophiles on the sulfur atom of the sulfone or sulfoxide group in acyclic or large-ring sulfones and sulfoxides is rather rare, or unknown, excluding metal hydride reductions and/or reductive deoxygenations. The situation is completely different in the three-membered ring systems. 

A nucleophilic attack of the hydroxide (or the alkoxide) ions on the sulfur atom of the thiirane dioxide ring to give sulfonic acids or similar intermediates, which then decompose to alkenes and bisulfite ion, has been suggested for these reactions16-17>". 

Whereas the reactions of sulfones with nucleophiles via pathways A and B of equation 1 are most frequently observed, the nucleophilic substitution reaction by pathway D has been observed only in the cases where the leaving carbanion can be stabilized, or in the highly strained molecules. Chou and Chang3 has found recently that an organolithium reagent attacks the sulfur atom of the strained four-membered sulfone in 34. When this sulfone is treated with 1 equivalent methyllithium, followed by workup with water or Mel, 38 or 39 are formed in high yield. 

Formation of cyclic sulfoxide (R)-55 by t reatment of bromoarene (i )-54 with tributylstan-nane apparently proves that intramolecular homolytic substitution at the sulfur atom of the sulfoxide group proceeds with strict inversion of configuration (equation 50)103. 

The absorption at 375 nm is assigned to the radical anion. OH radicals were found to give an optically active transient which absorbs at 360 nm and which is assigned by the authors to the radical anion formed by the reaction of OH with the sulfur atom of the thiomethyl bond of MTMSO,... 

The three-dimensional structure of oxytocin. The sulfur atoms of the disulfide bridge are in yellow. The ... 

TiCRjtftc) was prepared starting from Ti(NR2)4 4,5) or TiCl4 (6). The structure of the ethyl compound was elucidated by X-ray studies (7, S). The titanium atom is eight-coordinated by the sulfur atoms of the four chelating ligands and the coordination geometry closely approximates to that of a dodecahedron. 

A remarkable complex with the composition Co2(R2C fc)5BF4 resulted from an attempt of Hendrickson and Martin (81) to oxidise Co(R2r/tc)3- These authors report diamagnetic, ionic complexes, in which the metal atoms are bridged by two sulfur atoms of the ligands, as is found for Ru2(Et2(irc)5BF4 (77). 

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