Epoxides with triphenylphosphine

R. D. Guthrie, I. D. Jenkins, and R. Yamasaki, Epoxidation with triphenylphosphine and diethyl azodicarboxylate Epoxide derivatives of sucrose, Carbohydr. Res., 85 (1980) C5-C6. 

Guthrie, R D, Jenkins, I D, Yamasaki, R, Skelton, B W, White, A H, Epoxidations with triphenylphosphine and diethyl azodicarboxylate. Part 1. Synthesis of methyl 3,4-anhydro-D-tagatofuranosides, J. Chem. Soc., Perkin. Trans 1, 2328-2334, 1981. 

Trans alkenes are converted into their ds isomers and vice versa on epoxidation followed by treatment of the epoxide with triphenylphosphine. Propose a mechanism for the epoxide— alkene reaction. 

Epoxides can be converted to alkenes by treatment with triphenylphosphine or triethyl phosphite P(OEt)3. The first step of the mechanism is nucleophilic substitution (10-50), followed by a four-center elimination. Since inversion accompanies the substitution, the overall elimination is anti, that is, if two groups A and C are cis in the epoxide, they will be trans in the alkene ... 

A mixture of epoxides 483 obtained on oxidation of 482 with dimethyldioxirane, when exposed to ferric chloride provided, as the kinetically controlled product, the a-aldehyde 484, which without purification was reduced to the a-alcohol 485. The exclusive formation of 484 is believed to occur via the benzyl cation 486, generated by Lewis-acid opening of the oxirane ring, suffering a stereospecific kinetic 1,2-hydride shift The amino alcohol 487 obtained after sequential removal of O-benzyl and N-tosyl groups from 485, on treatment with triphenylphosphine and iodine in the presence of imidazole furnished the tetracyclic base 488, which was oxidised to the ketone 489. Trapping of the kinetically generated enolate of 489 as the silylether, followed by palladium diacetate oxidation yielded the enone 490. The derived... 

Finally, a valuable example of multistep modifications of sucrose is the synthesis of Sucralose (l Ab -trideoxy-l Ab -trichloro-tya/flcm-sucrose)—a compound 650 times more sweeter than sucrose,15,326,327 which was obtained by treatment of 6-O-acetylsucrose with sulfuryl chloride in pyridine. Further reaction of this derivative with triphenylphosphine and diethyl azodicarboxylate afforded an epoxide from which a tetrachloro-derivative... 

When the same conditions are applied to oxirane 5 azido alcohol 17 is formed this can be selectively reduced with triphenylphosphine to give amino alcohol 18 in good yield (Scheme 6.4.8 Eq. 2) [11, 25, 26], This compound and other, related, epoxides are a new approach to the chemistry of aminocarbasugars and their unsaturated analogs such as valienamine [27]. 

Androstenolone, 1, can be transformed microbiologically to the 7a,15a-dihy-droxy derivative 2 by the action of Colletotrichium Uni. During formation of the acetal (3), inversion takes place on C-7. Acidic cleavage of 3 results in the triol, 4, which can also be produced by direct acidic catalysis from 2 [12,13]. After selective protection to the 3/l,15a-dipivalate (5), the 15/1,16/1-methylene compound, 6, can be synthetized, and then stereoselectively transformed to the 5/ ,6/ -epoxide, 7. This reacts with triphenylphosphine and tetrachloromethane in pyridine to produce the 7a-chloro derivative, 8. On treatment with zinc and acetic acid, 8 can be converted to the key compound 9, which has a 5/i-hydroxy-6-ene structure. Compound 9 can then be methylenated stereoselectively in the 6/1,7/1 position by the Simmons-Smith method. The last three steps - 10 —> 11 —> 12 — drospirenone -include the build-up of the spironolactone ring, after which water is lost from the molecule and oxidation affords drospirenone. 

Synthetic utilization of sugar epoxides with the use of known Wittig modifications has been shown to be very useful.92,99 Thus, the alkene 15a and its 3-O-benzyl analog were resynthesized,92 albeit in moderate yields, by the interaction of epoxides 236a and 236b, respectively, with triphenylphosphine in boiling N,N-di-methylformamide. 

Reaction with epoxides. Epoxides react with triphenylphosphine and carbon tetrachloride (reflux under N2 for I 2 hr.) to give the corresponding cts-l,2-dichloro-alkane and triphenylphosphine oxide. Thus cyclohexenc oxide is converted into cis-l,2-dichlorocyclohexane in 80% yield. Only a trace of rran -l,2-dichlorocyclo-hexane is formed. 

Disubstituted peroxides are cleaved reductively by the same reagents as are used for hydroperoxides. The usual products are alcohols derived from the two substituents, but considerable selectivity is possible with some substrates. This is illustrated by the reduction of cyclic endoperoxides of the general formula (50) these compounds are available from the cycloaddition of singlet oxygen to cyclic conjugated dienes. The reduction of such compounds provides a good method of synthesis of cis-1,4-diols, which can be formed with retention of the double bond or with reduction of it (Scheme 29). It is also possible to prepare unsaturated epoxides by reduction with triphenylphosphine or other phosphorus(III) reagents. 

Levopimaric acid forms an epidioxide (63) which thermally rearranges to a di oxide (65). On photolysis the epidioxide gives both the diepoxide and the 12-keto-epoxide (64). Treatment of the epidioxide with triphenylphosphine affords a monoepoxide which was shown to be the 8a(14a)-epoxide (66). On further epoxidation this gave the diepoxide, levopimaric acid dioxide. The photochemistry of ring c diterpenoid y-hydroxydienones has also been investi-gated. " Thus compound (67 R = H or Et) afforded firstly the spiro-diketone (68) and then the unsaturated y-lactone (69). 

Epoxides react with triphenylphosphine dihalides to give r/c-dihalides. Some of the reactions are depicted in Scheme 2, but the stereochemical features... 

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). ... 

N-acylaziridines occurs on treatment with triphenylphosphine with the formation of the ylides (67), thereby providing a route to a-substituted primary allylic amines via their in situ reactions with aldehydes.The reactions of triphenylphosphine with epoxides in phenolic media provide a new access to the vinyl-phosphonium salts (68). A route to 1-hydroxyalkylphosphonium salts is provided by the reactions of trimethyl- or triethyl-phosphine with aldehydes or ketones in the presence of anhydrous acids. The related 1-trimethylsiloxyalkylphosphonium salts can be isolated in the presence of trimethylsilyl chloride.Further Wittig-products have been isolated from the reaction of 1,2,3-indanetrione with triphenylphosphine, and, in related work, it has been shown that furoin is deoxygenated on heating with triphenylphosphine to form 2-furfuryl(2-furyl)ketone and triphenylphosphine oxide.The structure of the blue product from the reaction of triphenylphosphine with 2,3,5,6-tetracyano-7-oxabicyclo(2,2,1]hepta-2,5-diene has now been shown by X-ray techniques to be the stable ylide (69). ... 

Reaction of the artificial sweetener sucralose (being 650 times sweeter than sucrose) with triphenylphosphine and diethyl azodicarboxylate afforded epoxide 102 from which the tetra-chloro-derivative 103 was obtained (O Fig. 25) [72]. 

As described above, 1,2-azido alcohols can be stereospecifically prepared from epoxides. 1,2-Azido alcohols thus prepared reacted with triphenylphosphine or trialkyl phosphites to afford aziridines, where inversion of both centers of the original epoxides takes place (Scheme Intramolecular oxirane... 

Alkenes are converted to epoxides by oxidation with peroxy acids, and thereby they are protected with regard to certain chemical transformations. Alkaline hydrogen peroxide selectively attacks enone double bonds in the presence of other alkenes. The epoxides can be transformed back to alkenes by reduction-dehydration sequences or using triphenylphosphine, chromous salts, zinc, or sodium iodide and acetic acid. A more advantageous and fairly general method consists, however, of the treatment of epoxides with dimethyl diazomalonate in the presence of catalytic amounts of binuclear rhodium(II) car-boxylate salts. This deoxygenation proceeds under neutral conditions and without isomerization or cy-clopropanation of the liberated alkene (Scheme 97). Furthermore, epoxides can be converted to alkenes with the aid of various metal carbonyl complexes. Thus, they may be nucleophilically opened with... 

On treatment with iV-bromoacetamide followed by alkali the olefin (46), a pyrolysis product of yV-isobutyrylcyclobuxidine F, afforded the corresponding 1/3,10/3-epoxide.The latter was readily transformed into (47) which was found to be identical with A -isobutyrylbuxaline F, an alkaloid from Buxus balearica. p-Nitroperbenzoic acid converted (48) into the la,10a-epoxide (49). Successive treatment of (49) with triphenylphosphine and sodium methoxide afforded the novel cyclopropane derivative (50). 

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