João V. Comasseto

Vinyllithiums from butyl-vinyl tellurides and bis-vinyl tellurides

Abstract Butyl vinyl tellurides and bis-vinyl tellurides furnish vinyllithiums with retention of configuration in good yields upon treatment with n-butyllithium at −78°C.

Addition of hydrogen halides to acetylenic selenides. Synthesis of 1-halo-1-selenoalkenes

Abstract Acetylenic selenides react with HX (X=Cl, Br, I) at room temperature to give 1-halo-1-selenoalkenes in good yields. The 1-iodo-1-selenoalkenes were transformed into the corresponding vinylic organometallics (M=Zn, Cu, Cr).

Stereoselective synthesis of vinylic selenides

Abstract The addition of selenophenol to mono - and di-substituted unactivated acetylenes have been investigated. At room temperature the vinylic selenides obtained were predominantly of the Z configuration; at 120°C Z/E mixtures were produced. Vinylic selenides with the E configuration were obtained by reduction of the corresponding selenoacetylenes with lithium aluminium hydride.

The reaction of selenenyl halides with wittig reagents

Abstract The transylidation reactions of PhSeBr with two equivalents of an alkylidene-triphenylphosphorane give selenophosphoranes, Ph3P=CRSePh. These also can be obtained by treating the corresponding selenophosphonium salts, prepared by quarternization of triphenylphosphine with PhSeCHRBr, with n-BuLi. The selenophosphoranes react with aldehydes in situ (Wittig reaction) to give the expected vinylic selenides in good yields. The stereochemistry of the reactions is discussed.

The reaction of selenophosphonates with carbonyl compounds. Vinylic selenides

Selenophosphonates of the general formula (EtO)2P(O)CHRSePh were prepared and their reactions with aldehydes and ketones investigated. The products formed are vinylic selenides having predominantly the E configuration. Hydrolytic cleavage of these products gives the corresponding ketones.

Coupling of Z-vinylic tellurides with alkynes catalysed by PdCl2CuI: synthesis of Z-enynes and Z-enediynes

Abstract Vinylic tellurides of the Z -configuration couple with alkynes under PdCl 2 CuI catalysis to give enynes and enediynes in good yields and with retention of the double bond configuration.

Synthesis of vinylic tellurides

Synthetic routes to vinylic tellurides employing nucleophilic and electrophilic tellurium species are described. Reaction of vinyl Grignard reagents with organotellurenyl bromides leads to vinylic tellurides (p-CH3OC6H4TeCHCHC6H5, p-CH3OC6H4Te(CH3)CCH2, n-C4H9TeCHCH2) in 71–86% yield; vinyltellurenyl iodides react with Grignard reagents to give vinylic tellurides (p-CH3OC6H4Te(CH3)CCH2, p-CH3OC6H4TeCH2, n-C4H9TeCHCH2) in 64–71% yield; trans-β-Bromostyrene react with p-CH3OC6H4Te− and n-C4H9Te− to give vinylic tellurides of trans configuration (p-CH3OC6H4TeCHCHC6H5, n-C4H9TeCHCHC6H5) in 86 and 83% yield, respectively; reaction of vinyl Grignard reagents with elemental tellurium followed by alkylation with n-bromobutane gives vinylic tellurides (n-C4H9Te(CH3)CCH2, n-C4H9TeCHCH2, n-C4H9TeCHCHCH3, n-C4H9TeCHCHC6H5) in 73–79% yield; divinyl ditellurides (C6H5CHCHTe)2, (CH3CHCHTe)2, (CH2CHTe)2, (CH2C(CH3)Te2) were prepared in 58–67% yield by reaction of vinyl Grignard reagents with elemental tellurium followed by air oxidation; divinyl ditellurides react with formamidinesulfinic acid in 50% sodium hydroxide under phase transfer conditions in the presence of n-C4H9Br to give vinylic tellurides (n-C4H9TeCHCHC6H5, n-C4H9TeCHCHCH3, n-C4H9Te(CH3)CCH2, n-C4H9TeCHCH2) in 81–86% yield; addition of n-C4H9Te− to acetylenes gives vinylic tellurides of cis-configuration (n-C4H9TeCHCHC6H5, n-C4H9CHCHCH2NCH2CH2OCH2CH2, n-C4H9TeCHCHCH2OCHOCH2-CH2CH2CH2CH2) in 78–93% yield.

Improved procedure for the hydrotelluration of alkynes

Abstract Z -Vinylic tellurides were prepared by hydrotelluration of alkynes with lithium butyl tellurolate generated by reaction of n -butyllithium with elemental tellurium.

Vicinal Difunctionalization of Alkynyl Selenides with Lithium Butylcyano Cuprate and Electrophiles

Abstract Alkynyl selenides react with lithium butycyano cuprate giving an intermediate lithium vinylcyano cuprate, which is trapped with electrophiles to give several classes of vinylic selenides.

Synthesis of (E)-1,4-bis(organyl) but-1-en-3-ynes by lithlium-tellurium exchange reaction on (Z)-1-butyltelluro-1,4-bis(organyl) but-1-en-3-ynes.☆

Abstract 1,4-bis)organyl)-1,3-butadiynes react with dibutyl ditelluride and sodium borohydride in ethanol under reflux to give (Z)-1-butyltelluro-1,4-bis(organyl) but-1-en-3-ynes, which by treatment with butyllithium followed by water give (E)-1,4-bis(organyl) but-1-en-3-ynes in high yields.