Stilbene oxide deoxygenation

Tiialkylsilyl metals, such as trimethylsilylpotassium," dimethylphenylsilyllithium, " and dimethyl-phenylsilyldiethylaluminum, " have been known to induce deoxygenation of epoxides. The reaction with TMSK and PhMe2SiLi proceeds with inversion of stereochemistry (Table 14) whereas PhMe2SiAlEt2 shows complete retention in the case of tran.r-stilbene oxide and cinnamyl alcohol epoxide. 

The reaction with (cyclopentadienyl)dicarbonylferrate can be directed to give either trans- or m-al-kenes simply by changing the reaction conditions. Thus, reaction with ci.r-stilbene oxide followed by treatment with sodium iodide in acetone gives m-stilbene, whereas only rranf-stilbene is obtained when the reaction is prepared at room temperature and is heated under reflux in THF (equation 47). Although deoxygenation of terminal epoxides proceeds very rapidly, internal epoxides require longer times. Consequently, as in equation (48), selective reduction of diepoxides can be carried out. 

Epoxides are stereospecifically deoxygenated to alkenes with inversion of stereochemistry upon treatment with PhMe2SiLi in THF.4 trimy-Stilbene is obtained in 83% yield and >99% stereoselectivity from the reaction of oxide of ciy-stilbene with PhMc2 SiLi. Similarly, irons-stilbene oxide is converted to c/s-stilbene. 

Deoxygenation of Epoxides. Fe(CO)5 in MA -dimethyl-acetamide or tetramethylurea deoxygenates epoxides (2 h, 145 °C). The reaction is not stereospecific franj-stilbene oxide is converted into both trans- (56%) and cw-stilbene (22%). Epoxides of 1-alkenes are converted mainly into mixtures of internal alkenes. 

A detailed study has been made of the base-catalysed deoxygenation of carbonyl compounds with diphenylphosphine oxide (52) at high temperatures. The known formation of good yields of frun -stilbene (56a) from benzaldehyde (53a) has been shown to involve the intermediate formation of cis- and mw5-stilbene epoxides, and their subsequent deoxygenation by (52). Similar deoxygenation of benzoylferrocene (53b) results in the formation of the ketones (54) and (55), as well as the hydrocarbons (56b) and (57). The rationalization given in Scheme 9 has been presented to explain these observations. ... 

Deoxygenation of epoxides. n-ButyUithium (2-3 eq.) reacts with ferric chloride in THF at -78° to form a black, soluble iron species that converts epoxides into olefins in about 60-90% yield. The reaction is not stereospecific for example, the oxide of c -stilbene is converted into cu-stilbene and trans-stilbene in the ratio 89 11. ... 

Deoxygenation of epoxides. Epoxides are converted into olefins by reaction with this reagent in THF at 20. The reaction is stereospecific. Thus the oxide of trans-stilbene is converted into c/j-stilbene (75% yield, >97% stereospecific), and the oxide of c/s-stilbene is converted into truns-stilbene (83%, yield, > 99%, stereospecific). 

Lithium reagents desulphurize /ra s-2,3-diphenylthiiran 1-oxide, but give about equal yields of cis-stilbene and the lithium salt of stilbene-cf-sulphenic acid with cis-2,3-diphenylthiiran 1-oxide. Decomposition of the trans-isomer in the presence of ylides (53) leads to small yields of sulphines. Pyridine iV-oxide is deoxygenated by SO. In all these cases, kinetic measurements show that decomposition of the thiiran 1-oxide occurs independently of the substrate. 

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