Oxirane deoxygenation

The deoxygenation of ethers by C atoms was first studied by McKay and Wolfgang who reported a high yield of in the reaction of with oxirane. Deoxygenation of oxrranes was subsequently reported for both arc and chemically... 

The earliest general method for the reductive deoxygenation of oxiranes to alkenes involved multistep procedures in which halohydrins were intermediates. Comforth, for example, used an oxirane deoxygenation in an early synthesis of squalene (Scheme 11). Diastereoselective double addition of ho-mogeranyllithium (23) to the dichloro diketone (24) gave the bis(chlorohydrin) (25), which was first converted to the diepoxide (26). Subsequent treatment with Nal and Zn in HOAc buffered with NaOAc gave squalene (27). 

Uses. Magnesium iodide is used in the deoxygenation of oxiranes into olefins and iodine. This step is important to organic chemistry because it helps in the stmcture elucidation of complex organic molecules (110). Eor example. 

Atomic carbon deoxygenates oxiranes (Scheme 37) (B-71MI50501, 76JA3820). Silylenes can also deoxygenate oxiranes (Scheme 38) (80JA1451). 

Attack on oxiranes by trivalent phosphorus (64HC(19-l)43l) provides a method of deoxygenation to alkenes with inversion (c/. Section 5.05.3.4.3(hY)) and this makes possible the interconversion of (Z)- and (f)-alkenes (Scheme 58) (B-74MI50505). Silicon nucleophiles behave analogously (76JA1265, 76S199). 

The pyrazine I reacts with singlet oxygen to yield the endoperoxide 2, which is converted into the 1,3,6-oxadiazepine 4 on treatment with triphenylphosphanc. It is thought that the reaction involves deoxygenation to the bicyclic oxirane 3 as the key intermediate.320... 

Usually, various quantities of alkane are found during the hydrogenolyses of oxacycloalkanes. This is especially so for the oxiranes on platinum metals in the presence of hydrogen. These alkanes presumably form from alkenes, which are formed from deoxygenation (Scheme 4.67). 

Dichlorocarbene reacts with oxiranes to produce dichlorocyclopropanes [18] via an initial deoxygenation reaction (Scheme 7.22). 

Deoxygenation of oxiranes with alkali 0,0-dialkyl phosphorotelluro-lates... 

The deoxygenation is stereospecific, the (Z)-oxiranes giving the (Z)-olefins. An epitel-luride has been postulated as the intermediate. 

Epoxides (oxiranes) can be reduced in different ways. So-called deoxygenation converts epoxides to alkenes. Such a reaction is very useful since it is the reversal of epoxidation of alkenes, and since both these reactions combined represent temporary protection of a double bond. 

Action of LTBH upon the 2,2 -ditosylate 94 afforded the known 3,3 -dideoxy sugar 100 less efficaceously, evidently because of competing, partial 0-desulfonylation which, however, provided as a benefit the new, unsymmetrical disaccharides 1Q2 and 103 (11 and 8%) that were formed via the monoepoxide 101. Compound 1Q2 was the main product of deoxygenation when the 2-monotosylato 95 was treated with LTBH, although anti-FUrst—Plattner opening of intermediary oxirane 101 is believed to have taken place as a minor side-reaction in this instance. 

The keto group of the trisubstituted dioxanone 133 generated by ozonolysis was removed by radical deoxygenation according to the Barton-McCombie protocol [80] via the alcohols 134 and the corresponding xanthate, leading after deben-zylation to the dioxane 135 in excellent yield. After conversion to the tosylate, cleavage of the acetonide and protection of the secondary alcohol function as a TBS ether provided access to oxirane 128 by cyclization with NaH in 99% yield and in virtually diastereo- and enantiomerically pure form (de, ee > 96%). 

Deoxygenation of epoxides Oxiranes are converted into alkenes with the same configuration by ISi(CH3)3 generated in situ. 

Sodium 0,0-diethyl tellurolophosphate deoxygenates terminal oxiranes quickly, cyclohexene oxide slowly, and trans-internal oxiranes very slowly2- 3. The yields of olefins are higher than 70%. 

These reactions can be carried out catalytically because the tellurium precipitated during the deoxygenation of the oxiranes will react rapidly with added sodium diethyl phosphite. Lithium 0,0-diethyl tellurolophosphate is a more powerful deoxygenation reagent and is able to convert certain internal epoxides to olefins in a stereospecific manner3. 

Oxiranes as Precursors to Carbenes/Nucleophiles. 3.6 Reductions. 3.7 Deoxygenations. 3.8 Oxidations... 

Heterolytic cleavage of oxiranes with Grignard reagents 89UK401. Stereospecific deoxygenation of epoxides to olefins 87H(26)1345. 

Oxiranes can be prepared by electrochemical oxidation. " Regioselective w-epoxidation of polyisoprenoids will take place with excellent yields on sodium bromide-promoted electrochemical oxidation in neutral or basic medium. " " This has now been described as a general method. " " Hexafluoropropylene oxiranes have been produced by electrochemical means. " The deoxygenation of dioxetane to oxirane with triphenylphosphine has been described (Eq, 50). ... 

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