Hydroxy-selenides, from epoxides

Allylic alcohols can also be obtained from epoxides by ring opening with a selenide anion followed by elimination via the selenoxide (see Section 6.8.3 for discussion of selenoxide elimination). The elimination occurs regiospecifically away from the hydroxy group.116 117 118... 

Epoxides can also be prepared from a variety of 3-functionalized alcohols such as p-hydroxy sulfoxides," p-hydroxysulfonium salts," P-hydroxy selenides" and vicinal diols. In the use of unsymmetri-... 

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. ... 

The unusual reactivity of selenoboranes towards epoxides gives new selective routes to /3-hydroxy-selenides and allyl alcohols.Thus, 1,2-epoxyoctane with B(SeMe)3 at 0°C for 0.7 h, followed by aqueous NaHCOa, gave (164) (81%) whereas the same reaction with styrene oxide gave (165) (63%) as the major product. For trisubstituted oxirans, however, the products were allylic alcohols, e.g. (167) (76%) from (166) on treatment with B(SePh)3 at 20 °C for 1.5 h. 

It is well known that a-seleno-alkyl-lithiums can be used for the formation of epoxides from ketones, but they are also valuable building blocks for the synthesis of higher homologues namely oxetans and tetrahydrofurans. The reactions proceed in a step-wise fashion via hydroxy-selenides (42), which are cyclized by reaction with bromine (Scheme 4). 

The reaction involving the alkylation of p-hydroxyalkyl selenides to give p-hydroxyalkylselenonium salts which are then cyclized with a base is by far the most general. It allows Ae synthesis of a large variety of epoxides such as tenninal, a,a- and a,p-disubstituted, tri-33-> and tetra-substituted, 3,i88 as oxaspiro[2.0.n]-hexanes, -heptanes and -octanes (Scheme 161, g Scheme 162, d Scheme 164, d Scheme 165, b) - and vinyl oxiranes (Schemes 166 and 181)33 -239 from both p-hydroxy-alkyl methyl33- 3 3 22>.222j36,263 phenyl selenides. ... 

Epoxides via methyl selenoacetals. Krief et al. have reported the synthesis of epoxides from two carbonyl compounds. The first step involves preparation of a dimethyl selenoacetal (1), followed by conversion to an a-methyl seleno-carbanion (a). These highly reactive carbanions react with even hindered carbonyl compounds to give 0-hydroxy methyl selenides (2), which are converted into selenonium salts by reaction with methyl iodide or dimethyl sulfate. 

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