Selenenyl halides bonds

Organotellurium(II) compounds can also contain a three-center, four-electron bond as shown for 39 to 42 in Fig. 19. Typically, these molecules contain an odd number ligands around the central atom and an electronegative atom helps to stabilize a tellurenyl halide or selenenyl halide bond through chelation to form a four, five, or six membered ring. " Such molecules are described as lO-Te-3 and lO-Se-3... 

Selenenamides (23) are obtained by the substitution of selenenyl halides with amines or by the metathesis of the former compounds with Af-silylamines. N-(Phenylseleno)phthalimide (24) is similarly obtained using potassium phthalimide (Scheme 10). These compounds can be isolated but are prone to hydrolyze when exposed to moisture. Selenenamides react with aldehydes or jS-dicarbonyl compounds to afford a-seleno derivatives (as in the process shown in equation 11), and add to activated double and triple bonds, as in the example in equation (19). The imide (24) is a useful alternative to PhSeCl in various selenenylation reactions, and to ArSeCN in the conversion of alcohols and carboxylic acids to selenides and selenoesters (8), as shown in Scheme 3. 

Generation of seleno carboxylates occurs instantaneously on treatment of selenenyl halides with carboxylic acids and, consequently, the phenylseleno-lactonization of unsaturated carboxylic acids by phenylselenenyl chloride may be formally considered as intramolecular addition of phenylselenenyl carboxylate to the C-C double bond. The reaction of 4-cyclohep-tene-l-carboxylic acid with phenylselenenyl chloride to give lactone 40 is a good example. 

A series of selenenyl compounds - selenenic acids, selenenic anhydrides, selene-nyl halides, selenocyanates, and selenenamides, etc. - act as excellent electrophilic selenenylation reagents toward a variety of carbon-carbon unsaturated compounds. For example, electrophilic addition of selenenyl halides to carbon-carbon double bonds proceeds stereospecifically in the anti conformation. This addition is first-order in both selenenyl halides and carbon-carbon unsaturated compounds. 

A series organotin tris(dithiophosphates) have been prepared from RSnCl, and Me2Sn(S2AsMe2)2 shown to be 4-coordinate. The Sn-Se bond is readily cleaved by selenenyl and sulphenyl halides, and by alkyl... 

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