1.5.9- triepoxides

As mentioned earlier, the McDonald group was able to extend their epoxide-domino-cyclization strategy to 1,5,9-triepoxides [10]. Indeed, they were successful in converting precursor 1-143 into the tricyclic product 1-146 in 52 % yield after hydrolysis (Scheme 1.36) [41]. As a possible mechanism of this polyoxacyclization it can be assumed that, after activation of the terminal epoxide by BF3, a sequence of intramolecular nucleophilic substitutions by the other epoxide oxygens takes place, which is induced by a nucleophilic attack of the carbonate oxygen, as indicated in 1-144 to give 1-145. 

An X-ray structure of 5yn-triepoxide (38) (74AG(E)539) shows that the cyclohexane ring is planar, with the three oxygens and sbt hydrogens lying in parallel planes 1.19 and 0.42 A respectively from the carbon plane. With all oxygens on one face , (38) forms a crystalline 2 1 complex with potassium iodide. 

Lindo-rv.ff oselecli ve oxacydization of polyepoxides is less common the first ster-eospedfic tandem endo-regioselective biomimetic oxacydization of polyepoxides to fused THP rings has only recently been reported [38a], The cyclization of the hydroxy-methoxymethyl-substituted triepoxide 75 (a 1,4,7-triepoxide), promoted and directed by La(OTf)3 through an intramolecular chelation and based on a procedure originally described for a monoepoxide system [38b], afforded the tri-... 

The tandem oxacydization of a triepoxide was also explored. On treatment with BF3 Et20, the famesol-derived triepoxide 84, with a tert-butylcarbonate as the nucleophilic terminating functional group, afforded the tricyclic bis-oxepane 85 as the major product (52%, Scheme 8.21). The tetraepoxide derived from geranylger-aniol was similarly converted into the corresponding tetracyclic structure [39a]. 

In China, the plant is used to treat rheumatic inflammation. The anti-inflammatory property is substantiated, and a surprising amount of evidence is available. Note that the main anti-inflammatory principle of Tripterygium uiildfordii is a diterpene triepoxide known as triptolide, which posseses potent anti-inflammatory and immunosuppressive properties (103,104). 

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. ... 

Simmons-Smith cyclopropanation of triene 423 delivers a triscyclopropyl hydrocarbon which exhibits chiral fluxional properties On epoxidation, a mixture of two triepoxides results these rearrange rapidly under a variety of conditions to 424, the first topologically nonplanar molecule The reaction path for this iso-... 

Triepoxide of p-aminophenol and glycidyl ether (Bakelite Division of Union Carbide Co.)... 

The synthesis of triphenylene triepoxide (18) in 10-55% yield has been accomplished by treating triphenylene with 6-20 equivalents of MCPBA in methylene chloride-aqueous sodium bicarbonate.14... 

In the case of benzene, a number of epoxides are known, e.g., mono-, di-, and triepoxides. All undergo interesting electrocyclic reactions. Benzene epoxide itself exists as a valence tautomer of 86 and 96.8 The enthalpy difference between the two forms is 1.7 kcal/mol. The activation energies for forward and reverse reactions are 9.1 and 7.2 kcal/mol, respectively. At room temperature the rate of exchange is so fast that the NMR spectrum is the average of chemical shifts that are due to protons represented by structures 86 and 96. 

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