Raney nickel deselenations

The deselenization of t-butyl phenylphosphinoselenoic acid by Raney nickel is highly stereoselective, allowing a stereochemical correlation between the selenoate and the analogous phosphorothioic acid through a common intermediate.125... 

A novel synthesis of an oxetane from a 1,4-diene by means of the new reagent PhSeOH has been reported. From 2,4-dimethyl-1,4-pe ntadiene there was obtained 2,4-dimethyl-2,4-bis(phenylselenomethyl)oxetane (65) in 34% yield. This compound can be deselenated with Raney nickel to 2,2,4,4-tetramethyloxetane (79JOC1742). 

Cyclizations by formation of carbon—selenium bonds represent a modern method with a high synthetic potential in the chemistry of cyclophanes. Selenocyanates such as 16 are accessible usually in excellent yields through the reaction of bromides with KSeCN [27], The reaction with benzylic bromides under reductive conditions using the dilution principle results in good to excellent yields of [3.3]di-selenacyclophanes which can be deselenized photochemically, pyrolytically (without previous oxidation), or by reaction with arynes, Stevens rearrangement and subsequent reaction with Raney nickel. [2.2]Metacyclophane (18), for example, is accessible in 47% total yield by using this sequence of reactions starting with... 

Selenides are also nucleophilic and produce isolable selenonium salts (9) when treated with alkyl halides. They are easily oxidized to selenoxides (10) and further to selenones (11) under more forcing conditions (see Section 4). Reduction of selenides to the corresponding hydrocarbons is most conveniently achieved with nickel boride,or with tri-n-butyl- or triphenyltin hydride under radical conditions. " Other reagents for reductive deselenization include Raney nickel, lithium triethylborohydride, and lithium in ethylamine (Scheme 4). Benzylic selenides undergo radical extrusion reactions under thermal or photolytic conditions to produce... 

Reviews devoted to Se chemistry or Raney nickel show that these are efficient reagents in reductive deselenations. Of course the advantages and drawbacks encountered with desulfurizations (see Section 4.3.1.2) must also be taken into consideration with deselenations. Raney Ni, often freshly prepared, is generally used in excess in solvents such as EtOH, ether, THE or DME, and under conditions milder than those for desulfurizations. From the numerous works published, it appears that the procedure tolerates alkyl and aryl ethers, - ketals, ketones, "" esters,"" lactones" and sulfonamides. A few representative examples are given in Scheme 18. 

Extensive studies are being conducted on a series of methylthio-pHirines, concerned with synthesis and effects of the methylthio-substituent upx>n structure and reactivity of other functions/ 6-Alkylseleno-9-0-i>-ribofu-ranosyl)purines are reductively deselenized to nebularine in near-quantitative yield with Raney nickel/ ... 

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