Oxabicyclo heptene

An example of the Diels Alder reaction of furans is the cycloaddition of 31 with 4,4-diethoxybut-2-ynal (32) which acts as an acetylenedicarbaldehyde synthon to afford 7-oxabicyclo [2.2.1]heptene derivatives [29] which were then converted into substituted cyclohex-l-ene-l,6-dicarbaldehydes by a four-step procedure (Scheme 2.14). 

Shortly after Trost s works, two investigations demonstrated the high reactivity of platinum halide salts for this type of reactions. Blum reported a PtCU-catalyzed rearrangement of allyl propargyl ethers to 3-oxabicyclo[4.1.0]-heptenes (Scheme 79).294 This series of reactions also represented the premiere entry into the versatile formation of cyclopropyl products based on skeletal rearrangements of enynes.295 This intriguing aspect is discussed further. 

The 7-azabicyclo[2.2.1]heptene derivative (57) decomposes in hot aqueous sodium carbonate solution to give A-benzylpyrrole-3,4-dicarboxylic acid and, presumably, ethylene. Furan-3,4-dicarboxylic acid derivatives are formed analogously on heating the 7-oxabicyclo-[2.2.1]heptene diesters (58). The only thermal decomposition of a... 

Compared to oxabenzonorbomenes, oxabicyclo[2.2.1]heptenes or oxabicyclo[3.2.1] octenes are less reactive substrates, and the Pd-catalyzed alkylative ring-opening process with organozinc reagents generally required heating in 1,2-dichloroethane at reflux. The addition of Zn(OTf)2 dramatically improved the rate of the reaction which could be carried out in CH2C12 at room temperature, as illustrated for the conversion of 83 to the... 

Dihydrobenzo[c]furan (136) has been prepared in a thermolysis reaction from 5,6-dimethylene-7-oxabicyclo[2,2.1]heptene (135) in benzene at ISO C. The mechanism of Scheme 2 accounts for this result. 

Figure 1.13 Functional Monomers Used for Monolith Grafting 7-Oxabicyclo[2.2.1]hept-5-ene-2-carboxylic acid (I), 7-Oxabicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic acid anhydride (II), and N-Phenyl-7-oxabicyclo[2.2.1]5-heptene-2,3-dicarboximide (III)...

Additional noncoagulating thromboxane agonist derivatives were prepared by the authors (1) in an earlier investigation. [15 -[la,2a-(Z),3P-(l , 3S, ) ta]]-7-[3-(3-hydroxy)-4-(4-iodophenoxy)-1 -butenyl]-7-oxabicyclo[2.2. l]hept-2-yl]-5-hepten-l -ol, (II), is especially preferred for treating acute angle-closure glaucoma. 

Chiral Auxiliary for Cycloaddition Reactions. Cam-phanate ester (11) has been used as a chiral dienophile in cycloaddition reactions with substituted furans to produce 7-oxabicyclo[2.2.1]heptene derivatives (eq ). ... 

CAB 3c derived from N-tosyl (a5 / )-/3-methyltryptophan catalyzes the Diels-Alder reaction of 2-bromoacrolein and furan with 96 4 enantioselectivity, enabling efficient synthesis of numerous chiral 7-oxabicyclo[2.2.1]heptene derivatives (Eq. 17) [18]. Interestingly, the analog 3b of catalyst 3c which lacks the y8-methyl group (derived from M-tosyl-(5)-tryptophan) is not as effective at catalyzing the formation of Diels-Alder product, and the reaction rate and yield are considerably lower. 

Treatment of the azabicyclo[2.2.1]heptene 580 with MCPBA for 3-5 s generated the oxabicyclo[3.2.1]octene 582 via a rapid Meisenheimer rearrangement of the A -oxide 581. Compound 582 was converted into the thermodynamically more stable isomeric bicyclic isoxazolidine 583 by simple heating (Scheme 142) <2000CC2451>. 

These reactivity patterns have been observed in various electrophilic additions to oxabicyclo[2.2.1]heptenes (Scheme 7). 

In addition to the examples shown above, Whalley reported one case of a hydrogenation reaction that resulted in the SN2 opening of an oxabicyclo [2.2.1] heptene [ 183 ]. In the presence of acid, substrate 229 was reductively ring opened to give 230 in quantitative yield, Eq. 141. 

The increased strain in oxabicyclo[2.2.1]heptenes such as 256b makes them more reactive toward organolithium reagents. The ring opening reactions occurred at lower temperatures and with higher regioselectivities, Eq. 187. 

Higher order cuprates also ring opened unsymmetrical oxabicyclo [2.2.1] heptene 298 with good regioselectivity, Eq. 198 however, no selectivity was observed in the reaction with unsymmetrical substrates such as 299, Eq. 199 [202]. 

In mid 1994, Hudlicky, et a/.,48 published a report describing the preparation of new synthons for C-disaccharides. The actual compounds of interest are the oxabicyclo[4.1.0]heptenes illustrated in Figure 8.13.1. Unlike the chemistry presented thus far, the compounds represented in Figure 8.13.1 were prepared utilizing the biocatalytic oxidation of haloarenes illustrated in Scheme 8.13.1.49.5o... 

With the preparation of the oxabicyclo[4.1.0]heptenes established, their use as synthons for C-disaccharides was explored. As shown in Scheme 8.13.2,... 

Oxabicyclo[2.2.1]heptene derivatives 21a and 2lb are conveniently prepared via the Diels-Alder reaction of cyanovinyl acetate with furan (see Section 1.6.1.1.1.2.2.2). These compounds add to cyclopentadiene (2) with very high exo selectivity. [4 + 2] Cycloaddition of cyclopenta-diene to 21a proceeds easily to afford a mixture of 22a and 23a with a d.r. (anti/syn) 93 7. Similarly, addition to 21b produces a mixture of 22b and 23b with a d.r. (anti/syn) 90 1023. 

R, 5R, 6R )-2-acetoxy-5,6-dibromo-2-cyano-S-oxabicyclo[2,2.1]heptene yield 54%... 

Butz and Sauer investigated the intramolecular Diels-Alder reaction of furfuryl fumarates 148 to synthesize oxabicyclo[2.2.1]heptene derivatives 149 and 150 (Scheme 8.37) [69]. Four new stereocenters of defined configuration are generated in this transformation under the induction of the stereogenic center in the side arm with remarkable selectivity. The cycloaddition of 148 with various substituents R at the stereogenic center was investigated and it was found that the diastereo-... 

From Benzo-7-oxabicyclo[2.2.1]heptenes, Benzo-7-oxabicyclo[2.2.1]heptadienes, and Related Compounds... 

Furans react with electron-deficient alkynes giving 7-oxabicyclo[2.2.1]heptadienes (30). Whereas it is possible to induce thermally a retro cycloaddition <62ioc3520.89CC1238>, normally these intermediates are reduced at the less hindered side, yielding 7-oxabicyclo[2.2.1]heptenes (31) (Scheme 30). Elimination of ethylene (Alder-Rickert reaction <37CB1354> yields substituted furans (Scheme 30) <6814501, 85JHC1233, 87BSF131>. 

Diels-Alder Reactions. Bp3-OEt2 is used to catalyze and reverse the regiospecificity of some Diels-Alder reactions, e.g. with pen-hydroxylated naphthoquinones, sulfur-containing conpounds, the reaction of 1-substituted trans-1,3-dienes with 2,6-dimethylbenzoquinones, and the reaction of 6-inethoxy-l-vinyl-3,4-dihydronaphthalene with p-quinones. BFs-OEta has a drastic effect on the regioselectivity of the Diels-Alder reaction of quinoline- and isoquinoline-5,8-dione with piperylene, which produces substituted azaanthraquinones. This Lewis acid is the most effective catalyst for the Diels-Alder reaction of furan with methyl acrylate, giving high endo selectivity in the 7-oxabicyclo[2.2.1]heptene product (eq 35). ... 

Oxanorbomenes are valuable substrates for RRM processes as weU [8], Thus, a smooth rearrangement of the 7-oxabicyclo[2.2.1]heptene 30 via domino ROM/ double RCM occurred on treatment with the second-generation Grubbs catalyst 2 under ethylene-free conditions (Scheme 2.12) [8b], The spiro compound 31 produced with high efficacy represents the DEF ring fragment of steroidal alkaloid cyclopamine. 

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