Disulfides, acyl alkyl

Alcoholysis of the acyl organyl sulfides RC(0)SxR (R, R =alkyl, aryl x=2, 3) in the presence of hydrogen chloride gives the organyl hydrodi- and hydrotrisulfides RSxH (x=2,3) in good yield [20,21,65,176,282]. Acyl alkyl disulfides react with thiols to yield asymmetrical disulfides [200]. Selenium bis(thiocar-... 

Cysteine sulfhydryls and cystine disulfides may undergo a variety of reactions, including alkylation to form stable thioether derivatives, acylation to form relatively unstable thioesters, and a number of oxidation and reduction processes (Figure 1.10). Derivatization of the side chain sulfhydryl of cysteine is one of the most important reactions of modification and conjugation techniques for proteins. 

Figure 1.10 Sulfhydryl groups may undergo a number of additional reactions, including acylation and alkylation. Thiols also may participate in redox reactions, which generate reversible disulfide linkages.

As in Section 5.06.9.1, the assignments are sometimes arbitrary. Important routes to oxadiazoles, aminooxadiazoles, oxadiazolinones, and oxadiazolinethiones involving the reaction of hydrazides RCONHNH2 with carboxylic acids, acyl chlorides, alkyl esters, or trialkyl orthoesters are described in Section 5.06.9.2.1, reactions with carbon disulfide... 

Amino groups react very easily with aldehydes or ketones, and with aldehydes in the presence of amines, they can be acylated by the usual acylating agents, and they react with amidacetals, Vilsmeier reagents and nitroso compounds (Scheme 12). As mentioned earlier, alkylation leads mainly to AT(2)-alkylated products. The hydrazino group reacts in the same way as the amino group with aldehydes or ketones, with acyl chlorides or carboxylic anhydrides, with sulfonyl chlorides, ortho esters, carbon disulfide and with nitrous acid. The last three reactions have mainly been used for the synthesis of condensed 1,2,4-triazines. 

Almost all electrophilic substitutions known to proceed in solution with isopropylbenzene can also be performed with polystyrene, using solvents such as nitrobenzene, carbon disulfide, or carbon tetrachloride. These substitutions include bromination [42], nitration [43,44], sulfonylation, Friedel-Crafts acylations [45 49], and alkylations... 

When R is an alkyl group, the 3-oxodithioesters available through sulfhydrolysis of the acylation products could not be prepared either by direct condensation of carbon disulfide on a ketone or via oxidation of the P-hydroxy dithioesters formed in the aldolization reaction of enethiolates (see Section 4.2.4). 

Acylation differs from alkylation in that the reaction usually is carried out in a solvent, commonly carbon disulfide, CS2, or nitrobenzene. Furthermore, acylation requires more catalyst than alkylation, because much of the catalyst is tied up and inactivated by complex formation with the product ketone ... 

The same photolytic treatment of O-acyl esters (2) in the presence of disulfides, diselenides, and ditellurides effectively produces the corresponding alkyl sulfides, alkyl selenides, and alkyl tellurides respectively, through SHi reaction on the chalcogen atoms by alkyl radicals, as shown in eq. 8.9. The reactivities somewhat depend on the kind of chalcogenides. Thus, the effective formation of alkyl sulfides requires 30 eq. of disulfides, that of alkyl selenides requires 10 eq. of diselenides, and that of alkyl tellurides requires 2 eq. of ditellurides [27, 28]. 

All types of electrophiles have been used with 2-lithio-l,3-dithiane derivatives, including alkyl halides, sulfonates, sulfates, allylic alcohols, arene-metal complexes, epoxides, aziridines, carbonyl compounds, imines, Michael-acceptors, carbon dioxide, acyl chlorides, esters and lactones, amides, nitriles, isocyanates, disulfides and chlorotrialkylsilanes or stannanes. The final deprotection of the dithioacetal moiety can be carried out by means of different types of reagents in order to regenerate the carbonyl group by heavy metal coordination, alkylation and oxidation184 or it can be reduced to a methylene group with Raney-nickel, sodium or LiAIII4. 

Lithiation of compound 560 with s-BuLi-TMEDA in THF at —78 °C following an inverse addition protocol provided the anion 561. It reacts with primary alkyl iodides and triflates, silyl chlorides, diphenyl disulfide, epoxides, aldehydes, ketones, imines, acyl chlorides, isocyanates and sulfonyl fluorides to yield the expected compounds 562 (Scheme 152). The transmetallation of compound 561 with ZnBr2 allowed the palladium-catalyzed cross-coupling reaction with aryl and vinyl bromides837. When the reaction was quenched with 1,2-dibromotetrafluoroethane, the corresponding bromide 562 (X = Br) is obtained838. 

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