Furan ring opening, oxidative

The ability to open the furan ring by oxidation has also been utilized for synthesis of trialkylacetic acids A 2-furoic ester is first subjected to a Friedel-Crafts reaction with a tertiary alkyl halide, and the 5-alkyl-2-furoic acid obtained from the product by hydrolysis is then oxidized by alkaline permanganate to the trialkylacetic acid 154... 

Hydrogen chloride/hydro gen peroxide Oxidative furan ring opening... 

In 1985 Whalley and co-workers reported the synthesis of pinselin (843) by a Lewis acid-mediated furan-ring opening/pyranone-ring closing of bromide 848, followed by oxidation of this alcohol, a-bromination, and aromatization with base to give pinselin (843) (588, 589) (Scheme 13.2)... 

Selective transformations Selective styrene ring opening [103] One-pot domino process for regioselective synthesis of a-carbonyl furans [104] Tandem process for synthesis of quinoxalines [105] Atmospheric oxidation of toluene [106] Cyclohexane oxidation [107] Synthesis of imines from alcohols [108] Synthesis of 2-aminodiphenylamine [109] 9H-Fluorene oxidation [110] Dehydrogenation of ethane in the presence of C02 [111] Decomposition of methane [112] Carbon monoxide oxidation [113]... 

A flexible entry into 2,4-disubstituted furan derivatives through condensation of the sulfur ylide derived from 20 with aldehydes, Pd-catalyzed opening of the vinyl oxirane thus formed, and a final oxidative cyclization of the furan ring was reported. Its utility was exemplified by the first total synthesis of the marine natural product ircinin-4 (21) <99SL29>. 

Ring opening is common in the alkali metal and liquid ammonia reduction of furans unless an anion stabilizing group is present, so most work has been done with derivatives of furancarboxylic acids. Treatment of furan-2-carboxylic acid with lithium and ammonia at -78 °C followed by rapid addition of ammonium chloride affords 2,5-dihydrofuran-2-carboxylic acid (80%). Reductive alkylation similarly gives 2-alkyl-2,5-dihydrofuran-2-carboxylic acids. This method has been used in a synthesis of rosefuran, the intermediate dihydrofuran (66) being converted into the product (67) by oxidative decarboxylation with... 

The formation of furans from pyrylium salts under oxidative conditions has been mentioned in Section 2.23.2.2. Ring opening and recyclization of 4-chloromethyl-2,6-dimethyI-pyrylium perchlorate (83) by aqueous alkali and DMF leads to 2-methylfuran-4-ylacetone (84) (77CHE918). When 2,3,4,5-tetraphenylpyrylium perbromide is hydrolyzed to the dienone and then subjected to bromination-dehydrobromination, 2-benzoyl-3,4,5-triphenylfuran (85) is formed. 

Ring cleavage in the furan system is usually obtained by catalytic hydrogenolysis. Examples are given in Section IV of addition reactions, and in Section VII of conversion reactions. Oxidative ring opening has already been described in a part of Section IV. 

Furans with suitable substituents in the 2-position can also be converted into phenols. These can be transformed into a 1,4-dicarbonyl system by 2,5 oxidation and ring opening. This system can then condense intramolecularly into a six-membered ring.333 334 The synthesis of m-hydroxybenzoic acid in 26% yield from furfuryl chloride288 is an example of this ... 

Oxidative ring cleavage of furan moieties to carboxylic acids under Sharpless conditions provided the paclitaxel side chain <03OL3987>, and amino acid derivatives <03HCA91>. An intramolecular ring opening of a furan derivative by an alkenyl radieal was attempted as an... 

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