Selenoxides reaction with aldehydes

Schemes 51-54) - (xiii) a-metallovinyl selenoxides (Scheme 179) (xiv) a-metalloalkyl selenones (Schemes 55 and 56) i29,i30,i38,206 gjjjj v) a-selenometalloenolates derived from esters (Scheme 10), lactones (Scheme 38), lactams - including B-lactams (Scheme 42, a Scheme 99), and nitroalkanes (Scheme 41). Most of the organometallics listed produce the corresponding alcohols by reaction with aldehydes and ketones and further hydrolysis of the resulting alcoholates. 

P-Hydroxy selenides are conveniently prepared from epoxides by treatment with sodium phenylse-lenide (Scheme 32) and by the addition of benzeneselenenic acid and its derivatives to alkenes (Scheme 33), - -" although in some cases these reactions are not regioselective. Useful phenylseleno -etherification and -lactonization reactions have been developed which can be regioselective (equation 42 and Schemes 34 and 35). -" " Selenide- and selenoxide-stabilized carbanions have been used in addition reactions with aldehydes and ketones, - and the reduction of a-seleno ketones also provides a route to P-hydroxy selenides. ... 

Reich has now described the ready preparation of a-lithio-selenides and -selenoxides, which smoothly condense with aldehydes and ketones. The resultant /3-hydroxy-selenides and -selenoxides can be reductively eliminated under very mild conditions to give tetrasubstituted olefins, which are not readily available from the Wittig reaction. The /3-hydroxyselenides can be converted into olefins under milder conditions than their sulphur equivalents, using methane-sulphonyl chloride in triethylamine. 

Conjugate addition of phenyl trimethylsilyl selenide to a,/3-unsaturated aldehydes and ketones has been attained by using triphenylphosphine, zinc chloride, or trimethylsilyl trifluoro-methanesulfonate as the catalyst. Combination of this reaction with selenoxide elimination provides a one-pot procedure for a-alkoxyalkylation of a,/3-unsaturated ketones (eq 3). 

Iodine-catalysed hydroperoxidation of cyclic and acyclic ketones with aqueous hydrogen peroxide in acetonitrile is an efficient and eco-friendly method for the synthesis of gem -dihydroperoxides and the reaction is conducted in a neutral medium with a readily available low-cost oxidant and catalyst.218 Aryl benzyl selenoxides, particularly benzyl 3,5-bis(trifluoromethyl)phenyl selenoxide, are excellent catalysts for the epoxidation of alkenes and Baeyer-Villiger oxidation of aldehydes and ketones with hydrogen peroxide.219 Efficient, eco-friendly, and selective oxidation of secondary alcohols is achieved with hydrogen peroxide using aqueous hydrogen bromide as a catalyst. Other peroxides such as i-butyl hydroperoxide (TBHP), sodium... 

Selenenyl halides are relatively stable, though moisture sensitive, compounds that are generally prepared by the reactions shown in Scheme 7 and behave as electrophihc selenium species. " They react with ketones and aldehydes via their enols or enolates to afford a-seleno derivatives (e.g. (17) in equation 11). Similar a-selenenylations of /3-dicarbonyl compounds, esters, and lactones can be performed, although the latter two types of compounds require prior formation of their enolates. Moreover, the a-selenenylation of anions stabilized by nitrile, nifro, sulfone, or various types of phosphorus substituents has also been reported (equation 12). In many such cases, the selenenylation step is followed by oxidation to the selenoxide and spontaneous syn elimination to provide a convenient method for the preparation of the corresponding a ,/3-unsaturated compound (e.g. 18 in equation 11). Enones react with benzeneselenenyl chloride (PhSeCl) and pyridine to afford a-phenylselenoenones (equation 13). 

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