Aryl benzyl selenides

Enantioselective conversions of aryl benzyl selenides to N-tosylselenimides 28 with [(tosylimino)iodo]benzene, cuprous triflate, and the chiral bis(oxazo-line) 22 have recently been demonstrated (Scheme 16) [37,38]. Because benzyl phenyl selenide undergoes uncatalyzed imidation with Phi = NTs in acetonitrile (46 % yield) or dichloromethane (trace yield), toluene was selected as the solvent for the asymmetric imidation reactions. Furthermore, in order to avoid racem-ization of 28 by moisture, molecular sieves were added to the reaction medium. 

Benzyl selenides exhibit a similar pattern of leactivi. Thus, although the parent aryl benzyl selenides are successfiilly metallated with LDA at -78 their higher homologs, as well as benzyl mediyl... 

The isolable and diermally staUe selenoxides are, dKiefore, rather limited. Stable examples are as follows those derived from selenides which have no hydrogen atoms on the p-carbon, such as dimediyl sel-enide, aryl methyl selenides, diaiyl selenides - and benzyl fdienyl selenides, those with an intramolecular hydrogen bonding, such as (36) and (37), and those leading to an unfavorable double bond such as (38). Vinylic selenoxides (39) and (40) are also generally isolable. 

Another application concerns the preparation of selenides and tellurides from diaryl diselenides ° or ditellurides. While selenide formation is carried out in refluxing toluene by using a large excess of diselenides, diaryl ditellurides give the best results by utilizing visible irradiation at 35 C. Aryl, benzyl, methyl, and dicyanogen selenides can be prepared in this way. 

Selenides (selenoethers)and tellurides can be prepared via RSe and RTe species, and selenium and borohydride exchange resin followed by the halide give the selenoether. The La/l2-catalyzed reaction of diphenyl diselenide with primary alkyl iodides gave arylalkyl selenides, and Inl has been used with benzyl halides. Diaryl selenides (Ar—Se—AF) have been prepared by couphng aryl iodides with tin reagents (ArSeSnR3) with a palladium(O) catalyst. ... 

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