Furan-ring derivatives

Grubbs and co-workers reported the first successful results of the inter-molecular cross-metathesis and intramolecular ring-closing metathesis with more reactive ruthenium catalyst for the a-functionalized olefins bearing ester, aldehyde, benzoyl or acetyl group. 

271a and 271b up to 99 1) and moderate yields were achieved through the Katsuki-Jacobsen oxidation-epoxidation of acyclic a-silyloxy sulfinyl dienes. This methodology for providing 2,5-traro-substituted sulfonyl dihydrofurans in good selectivity has been applied successfully in the formal syntheses of natural products. 

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Butin et al. reported that the indole derivative 29 was prepared by treatment of 2-tosylaminobenzylfuran 25 with ethanolic HCl in 78% yield. The furan ring served as the origin of a carbonyl group in this modification of the Reissert procedure. ... 

A biarylpropionic acid derivative containing a furan ring as a prominent feature has antiinflammatory activity. The patented synthesis involves a straightforward organometal1ic addition of ethyl lithioacetate to aldehyde 12 followed by saponification... 

Quaternary ammonium tribromides in methanol-dichloromethane did not brominate the furan ring of 3-methyl-8//-cyclohepta[/>]furan-8-one. Instead, the 7-bromo derivative was formed (92BCJ295). 

If on the other hand the polymerization of a furan derivative takes place through a substituent containing an adequate functionality, such as C=C or C=0, the furan ring should in principle conserve its structure and the polymers obtained will bear it as a side group. It has been found, however, that in some of these systems the normal propagation is accompanied by other reactions which involve participation of the ring and which therefore alter the normal structure of the macromolecule. The second section of this chapter deals with monomers, such as 2-vinylfuran and 2-furaldehyde, which exhibit this general behaviour. 

All the derivatives examined above owe their instability to the presence of the furan ring similar aldehydes, carbinols, chlorides, etc. bearing aliphatic and aromatic substituents are not prone to resinify. An analogous singularity of behaviour is encountered in furan polymers, as underlined at the beginning of this chapter. In a polymer prepared from a furan derivative three different situations must be considered ... 

Compound XI was shown to be an isomer of the derivative from D-glucose, differing from it in that the tetrahydroxybutyl chain is at the /3-position of the furan ring. Evidence for this structure is as follows. 

The propensity of the C5 site towards electrophilic substitution has been exploited to prepare functionalized oligomers by cationic polymerization. Thus monomers like isobutene, s ene, the vinyl ethers, etc. polymerize in the presence of simple furan derivatives such as 2-methyl furan to give essentially short chains (DP between 2 and 100 depending on the specific experimental conditions) with a terminal furan ring as a result of predominant transfer onto the C5 position of the added furan compound (20). 

Alkoxy radicals react easily with the furan ring the initial attack is not followed by rearomatization, but 2,5-dihydro derivatives are formed. Thus with f-BuOOH and Fe " " in methanol the reaction products were interpreted according to Scheme 16. 

In another variation, the intermediate aldol product 64, with an extra hydroxy group in the y-position, was used to construct the furan ring of rosefuran (65), a trace component of rose oil (Scheme 6.56) (285). Here, the reaction of the nitropentene derivative 61 with crotyl acetate (62) afforded the 3,4,5-trisubstituted isoxazoline (63) in moderate yield. Removal of the acetyl group by saponification of the cycloadduct, subsequent demasking of the aldol moiety using Mo(CO)6, and exposure of the ketodiol (64) to acid gave the target compound 65 (285). 

Reactions of this type have been used in the construction of the pyrrolylfuran derivatives (309) (R = H, 57% and R = C1, 24%) using nitrile ylides generated by the imidoyl chloride-KOf-Bu method (191). This reaction was a key step en route to simplified analogues of roseophilin, however, the reaction failed for the derivative with a methoxy group at the 4 position of the furan ring. 

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