Sulfur substitution

Several oxygen- and sulfur-substituted boranes have been reported (125—130). 1,3,2-Benzodioxaborole [274-07-7] (catecholborane, CB) (15) is the one best studied. It is commercially available or can be prepared by the reaction of catechol with borane-THF (57,131), or by other procedures (132). The product is a Hquid existing as a monomer, remarkably stable to disproportionation. No... 

Ana.lytica.1 Rea.gents, The chelating property of quinolines, eg, 8-hydroxy derivatives, make them useful in metal gravimetric appHcations however, few are any longer of practical importance. Amino- and sulfur-substituted quinolines have also been employed in metal analyses (105,106). 

The silicon- and sulfur-substituted 9-allyl-9-borabicyclo[3.3.1]nonane 2 is similarly prepared via the hydroboration of l-phenylthio-l-trimethylsilyl-l,2-propadiene with 9-borabicy-clo[3.3.1]nonane36. The stereochemistry indicated for the allylborane is most likely the result of thermodynamic control, since this reagent should be unstable with respect to reversible 1,3-borotropic shifts. Products of the reactions of 2 and aldehydes are easily converted inlo 2-phenylthio-l,3-butadienes via acid- or base-catalyzed Peterson eliminations. 

Another example of dynamic kinetic resolution is the reduction of a sulfur-substituted ketone. Thus, yeast reduction of (R/S)-2-(4-methoxyphenyl)-l, 5-benzothiazepin-3,4(2H, 5H)-dione gave only (2S, 3S)-alcohol as a product out of four possible isomers as shown in Figure 8.39c [29kj. Only (S)-ketone was recognized by the enzyme as a substrate and reduction of the ketone proceeded... 

The reduction of a-sulfur substituted ketone 27 and its analogues usually gives the anti-mercaptol alcohol like roc-14 which can be elaborated into cis-dihydrobenzoxathiin 30. 

The dynamic kinetic resolution (DKR) of a-sulfur-substituted ketones such as 31 and 33 was investigated. When the MOM protected mercaptol ketone 31 was treated with the BINOL-LiAlH4 complex, a moderate diastereoselectivity of 5 1 favoring the desired anti isomer was observed. The major diastereomer had 70%... 

Similar sulfur substitution, as in a fluoromethyl sulfide, also leads to deshielding, but somewhat less than for the analogous ether. 

Samarium(II) iodide also allows the reductive coupling of sulfur-substituted aromatic lactams such as 7-166 with carbonyl compounds to afford a-hydroxyalkylated lactams 7-167 with a high anti-selectivity [74]. The substituted lactams can easily be prepared from imides 7-165. The reaction is initiated by a reductive desulfuration with samarium(ll) iodide to give a radical, which can be intercepted by the added aldehyde to give the desired products 7-167. Ketones can be used as the carbonyl moiety instead of aldehydes, with good - albeit slightly lower - yields. 

Regiospecilic intramolecular cycloadditions of nitrones to sulfur-substituted dienes, with 3-sulfolene precursors, has been realized (Scheme 2.217). The stereochemical outcome of these reactions is affected by the structure of the substituent (sulfide or sulfone) in the diene and by the chain length connecting the diene and nitrone (a) and (b) (see Scheme 2.211). The bicyclic products obtained from these reactions have been converted to interesting heterocyclic compounds (709). 

Thioesterimide-haloborane adducts (c.f. Sect. VI.2, Eqs. (42-44)) can also be classified as imine-boranes. They are intermediated of low stability in the synthesis of monomeric sulfur substituted iminoboranes 27K... 

In general, sulfur-substituted allenes are accessible starting from alkyne precursors by a variety of transformations such as isomerization, rearrangement or addition reactions. The standard method for the synthesis of donor-substituted allenes is again the base-induced isomerization of alkynes. This very first method was applied for the preparation of achiral [11, 162, 163] and chiral [164] S-functionalized 1,2-dienes (Scheme 8.78). 

In addition to the sulfur-substituted enyne-allenes depicted in Schemes 20.18-20.20, the sulfoxide 141 was prepared by treatment of the enediynyl propargylic alcohol 108 with benzenesulfenyl chloride to induce a [2,3]-sigmatropic rearrangement (Scheme 20.29) [10]. The Myers-Saito cyclization of 141 occurs at 37 °C with a half-life of only 16 min. 

The reactions of thiosulfonates shown in general form in (167), and which constitute the majority of their chemistry, are, of course, substitution reactions at a dico-ordinate, or sulfenyl, sulfur. Substitutions of this type occur widely and with great frequency in the chemistry of all types of sulfenyl compounds. Because of their extreme importance in the chemistry of both thiolsulfonates and other sulfenyl derivatives, it is appropriate that we now review some of the major features regarding their mechanism that have emerged from the study of such reactions with various sulfenyl derivatives. 

C. Li, Sulfur-substituted and zinc-doped In(OH)3 A new class of catalyst for photocatalytic H2 production from water under visible light illumination, J. Catal. 237 (2006) 322-329. 

By far most of the reports on addition reactions of hetero-nucleophiles to activated dienes deal with sulfur-nucleophiles17,48,80,120-137, in particular in the synthesis of 7/3-sulfur-substituted steroids which, like their carbon-substituted counterparts (Section n.A), are of interest because of their ability to inhibit the biosynthesis of estrogens80,129-137. Early investigations17,120-122 concentrated on simple acyclic Michael acceptors like methyl sorbate and 2,4-pentadienenitrile. Bravo and coworkers120 observed the formation of a 3 1 mixture of the 1,6- and 1,4-adduct in the reaction of methyl sorbate with methanethiol in basic medium (equation 39). In contrast to this, 2,4-pentadienenitrile adds various thiols regioselectively at C-5, i.e. in a 1,6-fashion (equation 40)17,121,122, and the same is true for reactions of this substrate with hydrogen sulfide (equation 41), sodium bisulfite and ethyl thioglycolate17. 

The SRC-I process, developed by the Pittsburg Midway Coal Mining Co. in the early 1960s, was not really a hquefaction process rather, it was designed to produce a solid fuel for utility applications. Only enough liquid was produced to keep the process in solvent balance. The bottoms product was subjected to filtration or solvent extraction to remove ash and then solidified to produce a low-ash, low-sulfur substitute for coal. However, the value of the product was not high enough to make this process economically viable. 

Pl.l pro-Rp phosphoryl oxygen-sulfur substitution consistent with Mg + interactions seen in the Scott crystal structure (PDB 301D) obtained at pH 8.5, because the preceding NMR experiments were conducted at this pH. In the same NMR experiment conducted at pH 5.5, no Cd + shifts of the P NMR spectra were seen for the substrate Pl.l pro-Rp phosphoryl oxygen-sulfur substitution. 

Eliel et al. (72JA8587 76JA956) and Juaristi et al. (87JOC3806 90JOC33 92JA2157) studied the conformational behavior of 5-sulfur-substituted 1,3-dioxanes (see Table V) and discussed the results in terms of the rotamer population of the axial conformer in which steric, electrostatic, and stere-oelectronic effects are dominant. The sulfoxides place both the sulfinyl oxygen and the substituent outside the 1,3-dioxane ring in the sulfone, the position of the tBu substituent is similarly corroborated by an X-ray structure in the solid state. 

Studies on sulfur-substituted 2-pyridones have shown (99M545) that unsaturated phenylthio ketones 90 can yield aminopyrans 91 with MN 27a, while enaminone (X = NMe2) gives 2-pyridones 92 (Scheme 26). 

Studies with model alkenes indicate that the action of accelerators is to increase the extent of sulfur substitution (crosslinking) at the allylic positions of the diene polymer [Skinner,... 

Section 8.11.6.2.1) <2007ARK(viii)7>, and to the /ftt-amino effect <2006RCB384>. The intramolecular photocycloaddition of novel sulfur-substituted l,3-dioxin-4-ones (Equation 98) has been described <2006JA9040>. 

A reasonable mechanism for the iodine oxidation of 5-Trt cysteine peptides is given in Scheme 6. 45 Reaction of iodine with the divalent sulfur atom leads to the iodosulfonium ion 5 which is then transformed to the sulfenyl iodide 6 and the trityl cation. Sulfenyl iodides are also postulated as intermediates in the iodine oxidation of thiols to disulfides. The disulfide bond is then formed by disproportionation of two sulfenyl iodides or by reaction between the electrophilic sulfur atom of R -S-I and the nucleophilic S-atom of a second R -S-Trt molecule. The proposed mechanism suggests that any sulfur substitution (i.e., thiol protecting group) capable of forming a stabilized species on cleavage, such as the trityl cation, can be oxidatively cleaved by iodine. 

A weight percent asphalt in the conventional design R = sulfur substitution ratio... 

HEXAHYDRO - 4a,5 - DIMETHYL - 2(3H) - NAPHTHALE-NONE and 2-TRIMETHYLSILYLOXY-1,3-BUTADIENE AS A REACTIVE DIENE DIETHYL trans -4-TRIMETHYL-SILYLOXY-4-CYCLOHEXENE-1,2-DICARBOXYLATE. Sulfur substitution also continues to be of high interest, and three preparations on sulfide synthesis are included BENZYL SULFIDE DIALKYL AND ALKYL ARYL SULFIDES NEOPENTYL PHENYL SULFIDE and UNSYMMETRICAL DIALKYL DISULFIDES sec-BUTYL ISOPROPYL DISULFIDE. 

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