Selenones from selenoxides

Lithium enolates derived from methyl ketones and acetates successfully add to vinyl selenoxides - and to vinyl selenones to give cyclopropyl ketones and esters (Scheme 110). The a-lithioalkyl selenoxide or selenone intermediates presumably exchange to the lithium enolates which, after displacement of the seleno or selenoxy group, lead to the observed products. 

Additions of various nucleophiles to vinyl selenoxides - and vinyl selenones have been described. Thus potassium hydroxide and amines add to vinyl selenones and directly produce epoxides and aziridines, respectively, whereas 3-methoxyoxetanes have been obtained from 7-hydroxy-a-alkenyl selenones and st ium methoxide (Scheme 111). ... 

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. 

Schemes 51-54) (xiii) a-metallovinyl selenoxides (Scheme 179) (xiv) a-metalloalkyl selenones (Schemes 55 and 56) 29,i30,i38,206 a-selenometalloenolates derived from esters... 

Although unable to metallate selenides, dialkyl amides are sufficiently strong to metallate phenylselenoacetals39,46 51) as well as methyl48,52) and phenyl 46,47,52) selenoorthoesters. They are also able to metallate selenoxides 4 9,11 53 55) and selenones 14). Finally selenoacetals are readily available 4,711,12 S6) from carbonyl compounds and selenols in the presence of a Lewis acid and selenoorthoesters have been prepared from orthoesters, selenols, and boron trifluoride etherate47,48,52). 

The congeneric 0-acyl esters of iV-hydroxypyridine-2-selenone can also be prepared since the corresponding selenohydroxamic acid is readily available by treatment of 2-bromopyridine-iV-oxide with sodium borohydride and selenium. As shown in Scheme 11, this variant of the decarboxylative rearrangement, when followed by ozonolysis and subsequent selenoxide elimination, provided a useful route to optically pure L-vinylglycine from a protected glutamic acid derivative [16]. 

Vinylic ether-containing Claisen rearrangement substrates may be generated using syn-elimination reactions of sulfoxides, selenoxides, and selenones. 2-(Arylsulfinyl)ethyl ethers are particularly useful substrates in these reactions because of their ready availability by nucleophilic addition of allylic alcohols to commercially available phenylsulfinylethene. Scheme 13.27 shows a typical synthetic context for this chemistry, involving the stereospecific introduction of quaternary centers from easily accessed allylic alcohol precursors." ... 

The oxidation of (silatranyhnethyl)phenylselenide (116) with 30% hydrogen peroxide in ethanol affords the corresponding selenoxide (117a) in 91% yield (equation 146). The selenone 117b is formed by using 70% H202 . Unstable selenoxide is obtained from (2-silatranylethyl)phenyl selenide under the same conditions . ... 

Similarities are noted between the mass spectra of aliphatic and aromatic selenides with analogous sulphides and phosphines. " Selenoxides show the expected fragments derived from the selenate rearrangement product " " Extensions of these studies cover selenium dihalides (no moleculm ion is seen " ), seleninic acids and esters, " and selenones. Mass spectra of diaryl tellurides are very much like those of S and Se analogues. ... 

---