S-C bonds

Analysis We have an obvious Diels-Alder disconnection, some C-S bonds, and a 1,6-dicarbonyl relationship. The only one that gives any rapid simplification is the D-A, so we ll start with that ... 

Both C-S bonds are now P to carbonyl groups and so can be discomiected in turn by reverse Michael reactions. 

Another widely used route to cyclopropanes involves the addition of sulfoniutn ylides to a,/3-unsaturated carbonyl compounds (S.R. Landor, 1967 R. Sowada, 1971 C.R. Johnson, I973B, 1979 B.M. Trost, 1975 A). Non-activated double bonds are not attacked. Sterical hindrance is of little importance in these reactions because the C—S bond is extraordinarily long... 

In the presence of [PtC ] and a base. 2-aminothiazole undergoes ring cleavage of the C-S bond to give PtLCF (L=HSCH=CHNHCN) (699). The Pd and Pt complexes of 2-aminothiazoles show biological activity (1596i. 

The C-S bond in purine derivatives undergoes cleavage under mild conditions by nucleophilic agents such as benzylmercaptan or glutathione in dimethylformamide with a phosphate buffer of pH 6.5 (277). The salt (110) of dithiazolylsulfide heated at 190 C yields the A-4-thiazo-line-2-thione (112) and 2-chlorothiazole (111) (Scheme 56) (278-280). 

In Table 1-9 we have collected only the 7r-bond orders calculated by allvalence-electrons methods and compared their values with those deduced from experimental bond lengths. Both data are indicative of an aromatic molecule with a large dienic character. The 2-3 and 4-5 bonds especially present a large double-bond character, whereas both C-S bonds are relatively simple. 

F. 1-26. (a) ir-Bond order of the C-S bonds in the ground state, (fc) ir-Bond order of the C-S bonds in the first excited state, (c) Free-valence number of the intermediate diradicaf. (Most probable bicyclic intermediate resulting from the ring closure of the diradicai. 

This mechanism not only accounts for the substitution of the more labile chlorine atom on the polymer chain, it also results in the elimination of a new potential initiation site by moving the double bond out of conjugation with any adjacent chlorine atoms. The newly formed C—O or C—S bonds, with AH > 484 kJ/mol (100 kcal/mol), are significantly more thermally stable than even the normal C—Cl bonds in PVC at about 411 kj/mol (85 kcal/mol) (11). 

Most of the reactions of thiophosgene involve the expected chemistry of an acid chloride, in which the chlorine atoms are replaceable by various nucleophiles. A reaction involving the C=S bond is the Diels-Alder addition ... 

Manufacture. Trichloromethanesulfenyl chloride is made commercially by chlorination of carbon disulfide with the careful exclusion of iron or other metals, which cataly2e the chlorinolysis of the C—S bond to produce carbon tetrachloride. Various catalysts, notably iodine and activated carbon, are effective. The product is purified by fractional distillation to a minimum purity of 95%. Continuous processes have been described wherein carbon disulfide chlorination takes place on a granular charcoal column (59,60). A series of patents describes means for yield improvement by chlorination in the presence of dihinctional carbonyl compounds, phosphonates, phosphonites, phosphites, phosphates, or lead acetate (61). 

Oxidative Ring Closure Reactions 4.03.4.1.1 C—N bond formation N—N bond formation C—S bond formation N—S bond formation O—C bond formation O—N bond formation S—S, S—Se and Se—Se bond formation Electrophilic Ring Closures via Acylium Ions and Related Intermediates Ring Closures via Intramolecular Alkylations... 

Although evidence is not conclusive, indications are that the rearrangements are concerted. Heteroatom compositions required for the rearrangement are at least one N—O bond in the nucleus of the starting material and the formation of a C—N, N—N or C—S bond in the product (79AHC(25)147, p. 193, 81AHC(29)14l). 

JOC1537). The mechanisms of these transformations may involve homolytic or heterolytic C —S bond fission. A sulfur-walk mechanism has been proposed to account for isomerization or automerization of Dewar thiophenes and their 5-oxides e.g. 31 in Scheme 17) (76JA4325). Calculations show that a symmetrical pyramidal intermediate with the sulfur atom centered over the plane of the four carbon atoms is unlikely <79JOU140l). Reactions which may be mechanistically similar to that shown in Scheme 18 are the thermal isomerization of thiirane (32 Scheme 19) (70CB949) and the rearrangement of (6) to a benzothio-phene (80JOC4366). 

Schemes 110-113 outline the most common general methods for accomplishing the synthesis of thiiranes by formation of a C—S bond (75RCR138,66CRV297, 64HC(19-1)576). The methods in Schemes 111-113 are variations of Scheme 110 they differ in the details of the generation of the thiolate anion which effects the ring closure by a displacement reaction. The methods of converting oxiranes to thiiranes, to be discussed separately (Section 5.06.4.3), involve a displacement like thafof Scheme 110 as the final step.

The pA of 1,3-dithiane is 36.5 (Cs" ion pair in THF). The value for 2-phenyl-1,3-dithiane is 30.5. There are several factors which can contribute to the anion-stabilizing effect of sulfur substituents. Bond dipole effects contribute but carmot be the dominant factor because oxygen substituents do not have a comparable stabilizing effect. Polarizability of sulfur can also stabilize the carbanion. Delocalization can be described as involving 3d orbitals on sulfur or hyperconjugation with the a orbital of the C—S bond. MO calculations favor the latter interpretation. An experimental study of the rates of deprotonation of phenylthionitromethane indicates that sulfur polarizability is a major factor. Whatever the structural basis is, there is no question that thio substituents enhance... 

Attention should also be directed to the growing number of perfluorocarbon-sulfur species which feature single, double or even triple C-S bonds, e.g. ... 

Thiophene reacts with ReH7(PPh3)2 aided by the H-acceptor (3,3-dimethyl-l-butene) to give the thioallyl species 113 (92JA10767). Further reaction of 113 with trimethylphosphine yields organometallic products with a cleaved C—S bond. 

Thiophene reacts with [Cp Co(C2H4)] to cleave the C—S bond and yield 164 (920M2698, 97P3115). 

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