Diepoxides, rearrangement

The reaction of perfluoro-3,4-dimethylhexa-2,4-diene with calcium hypochlorite leads to the formation of a diepoxide, rearranging at 200 °C into the corresponding derivative of 1,4-dioxane (96RCI703). 

As described in the preceding paragraphs, oxidation products of carotenoids can be formed in vitro as a result of their antioxidant or prooxidant actions or after their autoxidation by molecular oxygen. They can also be found in nature, possibly as metabolites of carotenoids. Frequently encountered products are the monoepoxide in 5,6- or 5, 6 -positions and the diepoxide in 5,6 5, 6 positions or rearrangement products creating furanoid cycles in the 5,8 or 5, 8 positions and 5,8 5, 8 positions, respectively. Products like apo-carotenals and apo-carotenones issued from oxidative cleavages are also common oxidation products of carotenoids also found in nature. When the fission occurs on a cyclic bond, the C-40 carbon skeleton is retained and the products are called seco-carotenoids. 

The bicyclic peroxide 11 was prepared via diimide reduction of the endoperoxide derived from spirocyclopentadiene (Eq. 8)21>. As before, at elevated temperature the labile endoperoxide rearranges into diepoxide and ketoepoxide,22) but diimide reduction at —78 °C allows trapping leading to the highly strained bicyclic peroxide 11. 

Diepoxy-p-menthane, 6, rearranges when heated with alumina in toluene 73). What is the product of this reaction An organic chemist would predict that acid treatment of the diepoxide 6 (Figs. 3 and 32) would induce one or other of the oxirane rings to open. But which of the two will be the more reactive, and would overall reaction necessarily involve such an initial step Furthermore, for each oxirane there are two possible C—O cleavages. 

Diepoxidation of a diene Diepoxidation of the diene 1 with m-chloroper-benzoic acid gives a mixture of the d,l- and meso-diepoxides, whereas Sharpless epoxidation results in d- or 1-2 by a double asymmetric epoxidation. On treatment with base, 2 rearranges to the diepoxide a and then cyclizes to the meso-tetra-hydrofuran 3, a unit of teurilene, a cytotoxic C, -cyclic ether of red algae. This... 

The oxidative cyclization of allenyl alcohol 135 with a small excess of dimethyl-dioxirane leads to an intermediate diepoxide that rearranges to hydroxyfuranone 136 in 55% yield (Eq. 13.44) [52]. If the oxidative cyclization is conducted in the presence of 0.5 equiv. of toluenesulfonic acid, the major product is the furanone lacking the a-hydroxy group of 136. Hydroxyfuranones or pyranones are available from the same kinds of reactions of 5-methylhexa-3,4-dien-l-ol. 

Hexamethylbenzene reacts with DMDO via three pathways (i) to an arene oxide, which rapidly rearranges to an oxepin tautomer that then is oxidized to a cw-diepoxide and then to a cis, cis,trans-triepoxide (ii) a methyl group migrates in the first epoxide to give a cyclohexadienone, which then reacts to give a frani -diepoxide (iii) C—H insertion to give the benzyl alcohol and then the corresponding benzoic acid. ... 

Arylsubstituted cyclopentadienes such as 1,2,3,4-tetraphenylcyclo-pentadiene (369) give rise to isolable endoperoxides249 which can be thermally rearranged to m-diepoxides. From the corresponding fulvene derivative (372) only the diepoxide 374 was isolated which probably originates from a thermally unstable endoperoxide 37i.249,250... 

Oxetanones have been obtained from peroxy acid oxidation of f-butyl substituted allenes to form the allene diepoxide, which then either rearranged spontaneously, or upon addition of acid, to the 3-oxetanone in about 30% yield (equation 113). Thus the insertion of the ring oxygen between the ends of the allene system comes about indirectly. 

Conjugated cycloalkadienes4l3 17 are converted to bicyclic endoperoxides that may undergo thermal or photochemical rearrangement to yield diepoxides.374-377 1,3-Cyclopentadiene and 1,3-cyclohexadiene give endoperoxides exclusively. The first synthesis of the naturally occurring ascaridol (52) was also carried out in this way 418,419... 

As might be anticipated, when an O—O bond is cleaved in the presence of a radical trap, such as a double bond, the course of the reaction becomes quite different. Thus, thermolysis of bridged 3,6-dihydro-l,2-dioxins (1,4-endoperoxides) such as (146) causes rearrangement to c/s-diepoxides (147) <81T1825). 

Diepoxides react in the same manner as epoxides. Thus, perfluoro(1.2 5,6-diepoxyhexane) (3) rearranges to perfluoro(hexane-2.5-dione) (4).42... 

The photooxide of naphthalene (74) on treatment with triphenylphosphine is converted to naphthalene 1,2-oxide (45).40 The photooxide of anthracene (75) is converted to syw-anthracene[4a,10 9,9a]diepoxide (76) in 78% yield by means of an interesting photochemical rearrangement.41 The endoperoxide of... 

In contrast, peroxides with bridgehead alkoxy groups, such as 79 and 80, undergo the diepoxide photochemical rearrangement to diepoxides 81 and 82, respectively.42-44 The resorcinol derivative 83 on reaction with singlet oxygen... 

Thermal rearrangement of endoperoxides of bicyclic dienes gives syn-diepoxides [9b,33a], which are sometimes accompanied by epoxyketones... 

The p-peroxide 84 was obtained by methylene blue-sensitized photooxygenation of diene 83 together with its a-isomer (2 1 9,13-a p) and was separated by silica gel chromatography. Diepoxides are the thermally rearranged products of a.a -unsubstituted or alkylsubstituted furan endoperoxides [59,60d,g]. 

Rearrangement of 1,4-endoperoxides. Co l PP catalyzes the rearrangement of 1,4-endoperoxides to. syn-l, 2 3,4-diepoxides at - 78 Neither me.w-tetraphenylporphine nor zinc mexo-tetraphenylporphine catalyzes this rearrangement. N,N.N, N -Tetramethyl-ethylenediamine catalyzes the reaction, but only very slowly. The yields from the catalyzed reaction are much higher than those obtained by thermolysis. 

Addition to 3,S-cyeloheptadiene-l-oi (1). Photogenerated singlet oxygen (hematoporphyrin hydrochloride, sensitizer) adds to 1 in a stereoselective manner isyn to OH) to give mainly the endoperoxide 2. The reaction of the acetate of 1 is less selective because the acetyl derivative of 3 rearranges readily under both photolytic and thermal conditions to a diepoxide. Under the same conditions the acetyl derivative of 2 is relatively stable. ... 

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). 

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