Furans intermediate

Furan Derivatives Catalytic processes used to obtain furan derivatives from carbohydrates and the catalytic routes from furan intermediates to chemicals and polymers have been reviewed by Moreau et al. [27]. Some of the main reactions are summarized in Fig. 3.2. From fructose or carbohydrates based on fructose (sucrose, inulin), the first transformation step is dehydration to 5-hydroxy methylfur-fural (HMF). Fructose dehydration at 165 °C was performed in the presence of... 

Bisketenes can provide different reaction paths in the reaction with imines (Scheme 18). For example, bisketene (74) does not form p-lactam species like (76). Instead, DFT computations [78] indicate that zwitterionic intermediate (75) leads to the furane intermediate (77) whose cyclization yields aziridine (78). 1,2-, 1,3- and 1,4-bisketenyl benzene react normally to yield mainly bis (p-lactams) [78],... 

A special case where a racemic mixture can be converted to a single enantiomer was reported by Trost [137]. In this instance, the interconversion of the Jt-allyl complexes 44 and 45 is possible through a furan intermediate and the configuration of the product is controlled by the chiral ligand (Scheme 4). This... 

Carbohydrate-based adhesives, in which the formulation begins with the carbohydrate, have been reported (130), but the acid system used during formulation readily degrades the original carbohydrate to furan intermediates that... 

A variety of metal catalysts, based on metals such as Mo, W, Ru, Rh, Pd, and Pt, are available to cyclize enyne ketones (Equation 21). Initially, furan intermediates with a metal carbenoid substituent in the 2-position are formed which can be subjected to subsequent reactions furnishing furans with vinyl ether- <1998JOC4564>,... 

Diels-Alder reactions of oxazoles have proven to be quite versatile and continue to attract attention. Oxazoles have traditionally been used as the diene component and react with alkyne dienophiles to give furan products after extrusion of a nitrile molecule via a reverse-cycloaddition process. This method has been used to access highly substituted furans and has been utilized in numerous natural product syntheses. The reaction typically requires the use of high temperatures for efficient conversion. The furan intermediate 67 was obtained by a thermal intermole-cular Diels-Alder reaction between oxazole 66 and an acetylene. Furan 67 was a key intermediate for the synthesis of (—)-teubrevin G (Scheme 10) <2000JA9324>. Similarly, furan 68, obtained from a Diels-Alder reaction between 4-phenyloxazole and an acetylene, served as an intermediate in the total synthesis of the natural product cornexistin (Scheme 10) <20030L89>. 

Paterson, I.. Gardner, M., and Banks. B.J.. Studies in marine cembranolide synthesis. A synthesis of 2,3,5-trisubstituted furan intermediates for lophotoxin and pukalide. Tetrahedron. 45. 5283. 1989. 

Analysis of triene structures in leukotrienes or the dienes in the HETEs reveals in all cases that a cis,trans dienes (partial structure) is commonly shared. The Merck Frosst group has recently described a methodology for the delivery of cis,trans dienes in the synthesis of various HETEs. Scheme 2.9 depicts the basic route whereby a-diazoketones 25 react, via a carbenoid species, with furan to produce an unstable cyclopropyl furan intermediate 26. This reaction is efficiently... 

Anodendroic acid 68 has been isolated from Anodendron affine Durce while euparin 69 and pterofuran 70 have been obtained from Eupatoriumpurpureum and Pterocarpus indicus respectively. The synthesis of (+) anodendroic acid 6< , euparin 69 and pterofuran 70 also involves use of copper acetylide. The dihydrobenzo-furan, intermediate 67 has been converted to (+) anodendroic acid 68... 

Figure 19.2 Pathways for three key furanic intermediates with Co/Mn/Br mixtures in acetic acid.

From 17, the remaining retrosynthetic disconnections to readily available starting materials are relatively easy to deduce. First, syntheses of pyranones such as 17 are known to be possible through oxidative ring expansion of furan intermediates such as 18 mediated by a range of electrophilic species like dimethyldioxirane (DMDO), mCBPA, and A-bromosuccinimide. In turn, the bond between the furan ring and the adjacent hydroxy-substituted carbon atom could then be retrosynthetically cleaved to lithiated species 19 and its... 

For a possible route via a furan intermediate for the breakdown of the dehydrocellulose see Scheme VI. 

Three syntheses of the pseudoguaianolide ( )-confertin have appeared. Schultz uses the oxidation of an a-trimethylsilylated furan intermediate followed by reduction to give a butyrolactone during his synthesis. In another, the lactone (216), prepared by iodolactonization of the appropriate dimethyl amide, is converted into (217), using Bredereck s reagent (Scheme 114). In the third... 

It has been proposed by Zhao et al. [34] that the reaction follows two possible pathways (1) series of cyclic furan intermediates (A) (2) Open-chain pathway included formation of an enediol as an intermediate in the isomerization of glucose to fructose (B). 

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