Sulfenyl groups

The 5-(A -methyl-N -phenylcarbamoyl)sulfenyl group (Snm group) produced under these conditions is stable to HF or CF3SO3H. Since there are few acid-stable — SH protective groups, the Snm group should prove to be useful where strong acids are encountered in synthesis. 

A Fontana. F Marchiori, L Moroder, E Scoffone. New removal conditions of sulfenyl groups in peptide synthesis. Tetrahedron Lett 2985, 1966. 

In 2007, Hiemstra et al. established a catalytic asymmetric Pictet-Spengler reaction that proceeds via (V-sulfenyliminium ions (Scheme 15) [27], Treatment of iV-sulfenylated tryptamines 42 with aldehydes 40 and BINOL phosphate (R)-3f (5 mol%, R = 3,5-(CF3)2-CgH3) afforded tetrahydro-P-carbohnes. After completion of the cyclization the sulfenyl group was cleaved by the use of HCl. This one-pot... 

In conclusion, SNAr reactions are often facihtated by polar protic solvents such as butanol or by polar solvents in the presence of Brpnsted or Lewis acids. When displacements of halides with amines are used, both polar and protic solvents can solubilize the ammonium halides resulting from the reactions, and lead to the formation of Brpnsted acids. Fluoride or chloride ions are preferred leaving groups for this reaction. Suliinyl and sulfenyl groups require somewhat harsher conditions. 

Most of the clinically significant cephalosporin antibiotics possess a sulfenyl group at the C-3 position. The electrolytic ene-type chlorination products 2 are potent intermediates for the synthesis of 3 -substituted cephalosporins 6 (Scheme 2-2)8). 

Several medio are available for the intnxluction of sulfenyl groups a to carbonyl derivatives and these have been reviewed. - The most versatile procedure involves reaction of the enolate with an appropriate thiol derivative, but the preferred m od is largely dependent on the nature of the substrate employed (see below). In most instances, sulfur has been introduced in the divalent state and subsequently oxidized, although the oxidative step has been avoided by the direct introduction of sulfur at the S oxidation level. The oxidation of sulfides to sulfoxides is a trivial procedure that can be effected by a variety of reagents. Sodium metaperiodate, m-chloroperbenzoic acid and hydrogen peroxide are the most common oxidants, but r-butyl hydroperoxide, r-butyl hypochlorite, N-chlorobenzotriazole,... 

The a-sulfenyl group can be replaced by a benzothiazolthio group, as demonstrated in the synthesis of the 1,4-diketone (CXXXIV), a precursor of cw-jasmone [Eq. (65)] [10]. The geminal dicarboxylic acid (CXXXVI) can also be transformed into the 1,4-diketone (CXXXIV) by electrochemical decarboxylation as in Eq. (66) [6], suggesting that the substituted malonic acid group is synthetically equivalent to a carbonyl group. 

The pJCt value for 2-CHz of 1,3-dithiane is 31.1, indicating that the sulfenyl group stabilizes the adjacent carbanion. Theoretical studies present convincing evidence for the unimportance of d-orbital participation in the acidification of C—H bonds a to sulfur atoms. Whether or not 3d-orbitals are included in Ae basis set, the preferred conformation of CH2 H is predicted to be that of an sp carbanion (2). The calculation, NMR studies and crystallography all support a tetrahedral structure for the a-lithiated sulfide. ... 

Sulfenylation." Quinone mono-O.S-acetals are donors of sulfenyl groups to enable introduction of such substituents to ketones in the presence of MOjSiOTf. 

W-Hydroxybenzotriazole, trifluoroethanol, rt/ Trityl and Nps (2-nitrophenyl-sulfenyl) groups are also cleaved under these conditions. 

Compounds with fungicidal properties containing a polyhali en alkanoic sulfenyl group... 

A spirocyclic dithiolactone 65 was synthesized in high yield by sulfenyl group-assisted dehydration followed by intramolecular cyclization of P-hydroxy y-(phenylthio) dithioate66 (Scheme 16) [52,53]. 

Several sulfenyl group sources are also known [60,61]. Diphenyl selenide was reported [52]. Diphenylphosphorus chloride was used extensively in the synthesis of new phosphines [38,47,51,62]. A chiral version is shown in Eq. (6) [51]. 

The route seenos to be general for synthesis of unsymmetrical ketones bearing a sulfenyl group on only one CHe group, a type that is not generally readily available by direct sulfmylation. ... 

B. CHIRAL LIGANDS CONTAINING SULFENYL GROUPS B.i. Oxazoline Ligands... 

Chiral amidine ligands bearing sulfenyl groups have been developed.ui In these cases, more electron-rich imino groups (amidines) improve the enantioselectivity and the catalytic activity in Pd-catalyzed allylic substitution in comparison with oxazolines. 

ProIine-derived phosphines bearing various sulfenyl substituents have been developed Use of 21a-g as chiral ligands provided (5)-2, except 21e [(/ )-2], with 31-88% ee in the Pd-catalyzed allylic alkylation of 1 with dimethyl malonate using [Pd(7r-allylX l]2, BSA, and AcONa in dichloromethane at room temperature. Increasing the steric bulk of the substituents of the sulfenyl groups results in enhanced enantiocontrol (21g. provides 88% ee). The thiophene ligand 22 provides (R)-2 with 30% ee (Scheme 12). 

---