Diselenides, reactions with alkynes

Introduction of two different chalcogen elements to the C-C unsaturated bond is of particular interest from both synthetic and mechanistic viewpoints. Therefore, extensive studies have been carried out on the development of the (RE)2/(R E )2 binary system without using RE-E R compounds, which are difficult to prepare. (Z)-l-Seleno-2-thio-1-alkenes are produced regio- and stereoselectively when a mixture of diaryl disulfides and diaryl diselenides is subjected to a rhodium-catalyzed reaction with alkynes (Equation (68)).193... 

Irradiation of a mixture of diphenyl disulfide and diphenyl ditelluride in the presence of vinyl cyclopropane 141 with visible light gives the ring-opened thiatelluration product 142 as an E/Z mixture.208 Similar reaction with alkynes gives the thiatelluration product 143. The product stereochemistry depends on the nature of the alkyne.208 A mixture of diphenyl diselenide and diphenyl ditelluride reacts with alkynes in a similar way (Scheme 78).208 Similar reactions with allenes are less satisfactory.209... 

Table 3 Palladium-catalyzed reactions of disulfide and diselenide with alkynes...

Another method for the fluoroselenylation of alkynes is the reaction with xenon difluoride and diorganyl diselenides, for example the formation of 1 and 2. - ... 

Diarylchalcogenides have also been used as a source of ArS and PhSe in the carbonylation of alkynes [13]. Having established that Pd(PPh3)4 catalyzes the stereoselective addition of diaryl disulfides and diselenides to terminal alkynes to afford (Z)-l,2-bis(arylthio)-l-alkenes and (Z)-l,2-bis(arylseleno)-l-alkenes, respectively, the reaction was conducted under carbonylative conditions to afford the corresponding (Z)-l,3-bis(arylthio)-2-alken-l-ones and (Z)-l,3-bis(arylseleno)-2-alken-l-ones 8 with excellent levels of regio- and stereocontrol such that CO was incorporated at the terminal carbon of the alkyne and the Z-isomer favored with selectivities of 94—100% (Equation 10.5). Two pathways were considered on the basis of the regio- and stereoselectivity of carbonylation one involving the insertion... 

Addition of diphenyl disulfide (PhS)2 to terminal alkynes is catalyzed by palladium complexes to give l,2-bis(phe-nylthio)alkenes (Table 3)168-172 The reaction is stereoselective, affording the (Z)-adducts as the major isomer. A rhodium(i) catalyst system works well for less reactive aliphatic disulfides.173 Bis(triisopropylsilyl) disulfide adds to alkynes to give (Z)-l,2-bis(silylsulfanyl)alkenes, which allows further transformations of the silyl group to occur with various electrophiles.174,175 Diphenyl diselenide also undergoes the 1,2-addition to terminal alkynes in the presence of palladium catalysts.176... 

An interesting three-component reaction occurred when a solution of diphenyl diselenide (SI), an electron-deficient alkyne (e.g., ethyl propiolate), and an excess of an isocyanide (SO) was irradiated through Pyrex with a tungsten lamp (hv > 300 nm). The reaction is based on a selective sequentially radical addition, as illustrated in Scheme 3.33, and the coupling products were formed in 58-85% yield [83], As for the example reported in Scheme 3.33, the elaboration of compound 52 yielded a precursor for the construction of the carbapenem framework. 

Acetoxylation. Transformations of Carbonyl Compounds. Phenolic Oxidation. Oxidation of Nitrogen Compounds. Hypervalent iodine Reagents in Combination with Azido Compounds. DIB and Sodium Azide in Combination with Other Reagents. Transformations of Alkynes Involving Thiophenols and Diphenyl Diselenide. Miscellaneous Reactions. 

Similar reactions were also achieved by the formation of diastereomeric optically active selenoxides as intermediates in the elimination reaction. Optically active ferrocenyl diselenide 19 was used in selenenylations of alkynes generating vinyl selenides of type 164. Oxidation of the selenides was performed with mCPBA under various reaction conditions which afforded the corresponding chiral selenoxides, which, after elimination, afforded axial chiral allenecarboxylic ester derivatives 165 in high enantioselectivities (R = Me 89% ee, R=Et 82% ee, R = C3H7 85% ee) (Scheme 47)>85 87... 

Upon irradiation, thiyl radicals are generated and add to the alkyne 148 (the corresponding selenyl radicals are also formed but are less reactive than the thiyl radicals). The vinyl radical 149 cyclizes to 150. Finally, 150 reacts with diphenyl diselenide, the best radical trap present in the reaction mixture, to afford the product 151. 

The fluorination of alkenes 41 and 43 and alkynes 45 with difluoroiodotoluene in the presence of iodine affords vt c-fluoroiodoalkanes 42 and 44 and fluoroiodoalkenes 46 in moderate to good yields (Scheme 3.16) [40]. This reaction proceeds in a Markovnikov fashion and with prevalent an//-stereoselectivity via initial addition of the electrophilic iodine species followed by nucleophilic attack of fluorine anion. The analogous reaction of alkenes and alkynes with difluoroiodotoluene in the presence of diphenyl diselenides affords the respective products of phenylselenofluorination in good yields [41],... 

The catalytic cycle suggested for this reaction involves oxidative addition of to Pd(0) with formation of Pd disulfide or diselenide, alkyne coordination and insertion into the Pd-Z bond and reductive elimination (Scheme 3.60). 

However, the same complex catalyzed stereoselective addition reaction in the mixture of alkyne with diaryl disulfide and diphenyl diselenide (Scheme 3.77) [126]. 

The Pd(PPh3)4-catalyzed reaction of terminal alkynes with diaryl disulfide or diaryl diselenide under pressurized carbon monoxide is found to lead to the regioselective introduction of carbon monoxide to the terminal position of the alkynes with excellent stereoselectivity, as shown in Scheme 6. ... 

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