Vinyl selenide

Diseleno acetals and ketals are cleaved more rapidly than their dithio counterparts a methyl derivative is cleaved more rapidly than a phenyl derivative. Methyl iodide or ozone converts diseleno acetals and ketals to vinyl selenides. ... 

A solid-phase synthesis of 3-substituted isoxazoles 31 in good yields and purities was achieved by 1,3-DC of polymer-supported vinyl selenide with in situ generated nitrile oxides treatment of intermediate isoxazolines 30 with an excess of hydrogen peroxide resulted in the release of isoxazoles 31 while the use of Mel/Nal led to 3-substituted 5-iodoisoxazolines... 

This regioselectivity is practically not influenced by the nature of subsituent R. 3,5-Disubstituted isoxazolines are the sole or main products in [3 + 2] cycloaddition reactions of nitrile oxides with various monosubstituted ethylenes such as allylbenzene (99), methyl acrylate (105), acrylonitrile (105, 168), vinyl acetate (168) and diethyl vinylphosphonate (169). This is also the case for phenyl vinyl selenide (170), though subsequent oxidation—elimination leads to 3-substituted isoxazoles in a one-pot, two-step transformation. 1,1-Disubstituted ethylenes such as 2-methylene-1 -phenyl-1,3-butanedione, 2-methylene-1,3-diphenyl- 1,3-propa-nedione, 2-methylene-3-oxo-3-phenylpropanoates (171), 2-methylene-1,3-dichlo-ropropane, 2-methylenepropane-l,3-diol (172) and l,l-bis(diethoxyphosphoryl) ethylene (173) give the corresponding 3-R-5,5-disubstituted 4,5-dihydrooxazoles. 

Cross-coupling reactions of vinyl zirconocenes of general structure 41, mainly using group 10 metal catalysts, can be smoothly effected to give a variety of vinyl selenide-con-taining materials, which are amenable to further elaboration through nickel-catalyzed... 

The reaction furnishes low yield (owing to the low Al/Te exchange in the A1 vinyl intermediate and the formation of (Z)-vinyl selenides as by-products) leading therefore to introduce a valuable alternative based on a hydrozirconation protocol. 

Reaction of (trimethylsilyl)vinyl selenide 122 with methyl vinyl ketone catalyzed by SnCLt gives the [2 + 2] adduct 123 in 66% yield (equation 51)176. Replacement of the MegSi group with a hydrogen atom or a methyl group produces a complex mixture. Thus, the MesSi group can suppress side reactions by its steric effect. 

Experimental and theoretical studies of the gas-phase protonation of vinyl ethers, vinyl sulphides and vinyl selenides show, in conflict with the previous studies, that SMe and... 

I - Alkyny lphenyl selenides. Benzeneselenenyl bromide and silver nitrite (1 equiv.) rcncl to form a reagent (presumably C6H5SeN02) that converts 1-alkynes into 1-nlkynyl phenyl selenides (equation I).1 The same reaction has been effected in generally lower yields with phenyl selenocyanate catalyzed by Cu(I).2 The products tire useful intermediates for regio- and stereoselective synthesis of vinyl selenides. 

Selenones/ y-Hydroxy vinyl selenides (1) are labile and readily undergo dehydration on standing, but can be oxidized successfully to y-hydroxy vinyl selenones (2) by m-chloroperbenzoic acid in the presence of K2HP04 in CH3OH at 25°. 

Vinyl selenides, ketene selenoaeetals. Methyl selenoacetals (1) derived from ketones are converted into vinyl selenides on reaction with P2I4 or PI3 and triethylamine in CH2C12 at 25° (equation I). The sulfur analogs undergo the same reaction. 

Pentacarbonyl(trimethylsilyl)manganese. VINYL FLUORIDES Pyridinium poly(hydrogen fluorideV-N-Bromosuccinimide. VINYLPHOSPHINES 2,4,6-Trii sopropy I benzenesulfonylhy drazine. VINYL SELENIDES Benzeneselenenyl halide-Silver nitrite. Diphosphorus tetraiodide. 

DMAD and methyl propiolate to give the pyrazolylvinyl vinyl selenides 246 (ca. 61% from crude salt 139) and 247 (ca. 51% from crude 139). On the other hand, the intramolecular rearrangement of 3,5-diphenyl-l,2,4-selenadiazol-2-ium-2-ylmethanide 248 occurred more rapidly than cycloaddition and no trapping was achieved with up to 20 mol excess of dimethyl acetylenedicarboxylate. The rearrangement gave 4,6-diphenyl-2//-l,3,5-selenadiazine 250 in 79% yield. 

Trialkylboranes were converted into alkyl phenyl selenides and alkyl phenyl tellurides by reactions with PhSeSePh and PhTeTePh in the presence of stoichiometric amounts of air.550 Vinyl selenides and tellurides were synthesized by treating vinylboronic acids or esters with phenylselenyl chloride in ionic liquids (Equation (114))551 or by palladium-catalyzed coupling reaction of diorgano ditellurides (Equation (115)).552... 

Selenium-containing molecules have also been used as precursors for radical seleno group transfer reactions. This is a very powerful method for radical additions to alkenes and alkynes it is especially interesting from an atom economy point of view since all atoms remain in the product molecule. The free-radical addition of selenosulfonates 146 can be initiated either photochemically or thermally using AIBN. The addition of 146 not only to alkynes 147,255-257 km also to alkenes258-261 or allenes,261 has been reported and the products such as 148 are versatile building blocks for subsequent reactions (Scheme 39). For example, vinyl selenides 148 can be easily transformed into allenes. 

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... 

The hydrozirconation of alkynylselenides 99 has been applied to prepare mixed vinylic selenides and tellurides, (e.g., 100) and selenotelluroketene acetals (e.g., 101) (Scheme 62).179... 

Vinyl selenides have been lithiated at the a-position by LDA983,984 at —78 °C in THF to give a-(arylselanyl)vinyllithiums 680, a-(methylselanyl)vinyllithiums 681 being obtained by selenium-lithium transmetallation from l,l-bis(methylselanyl)alkenes with n-BuLi in THF or t-BuLi in ether at —78 °C985 986. These intermediates reacted with alkyl halides, epoxides, carbonyl compounds and DMF985, the final deprotection being performed by mercury(II) salts986. 

The synthetic utility of this base (1) was demonstrated in the preparation of vinyl iodides in high yields from simple ketohydrazones and iodine (Table), a process that normally gives mixtures of vinyl iodides and geminal diiodides if less hindered bases are employed.6 This base has also been used in the elimination of sulfonic acids from the corresponding sulfonates, the alkylation of compounds containing active methylene groups, the conversion of hydrazones to vinyl selenides, and the preparation of esters from sterically hindered acids.4 5... 

Use of benzeneselen nyl bromide as the electrophile in this reaction provides phenyl vinyl selenides in 70-90% yield. 

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