2.5- Diacetoxy-2,5-dihydrofuran

The original preparation of y-crotonolactone by Lespieau involved a five-step sequence from epichlorohydrin and sodium cyanide. A recent detailed study of this procedure reported an overall yield of 25% for the lactone. Glattfeld used a shorter route from glycerol chlorohydrin and sodium cyanide hydrolysis and distillation of the intermediate dihydroxy acid yielded y-cro-tonolactone in 23% yield and -hydroxy-y-butyrolactone in 28% yield. The formation of y-crotonolactone in 15% yield has also been reported from pyrolysis of 2,5-diacetoxy-2,5-dihydrofuran at 480-500 . ... 

Bromine or electrolytic oxidation of furan in alcoholic solution gives the corresponding 2,5-dialkoxy-2,5-dihydrofuran 159 (R = Alk). Lead tetraacetate in acetic acid oxidation yields 2,5-diacetoxy-2,5-dihydrofuran 159 (R = Ac). 

Methoxy- and 2-acetoxyfurans are available from 2,5-dimethoxy- and 2,5-diacetoxy-2,5-dihydrofurans (section 15.1.4) via acid-catalysed elimination. They undergo Diels-Alder cycloadditions the adducts can be further transformed into benzenoid compounds by acid-catalysed opening. 3,4-Dihydroxyfuran is undetectable in tautomeric equilibria between mono-enol and dicarbonyl forms the dimethyl ether behaves as a normal furan, undergoing easy a-electrophilic substitution, mono-or dilithiation at the o-position(s), and Diels-Alder cycloadditions.2,5-Bis(trimethylsilyloxy)furan is synthesised from succinic anhydride it too undergoes Diels Alder additions readily.Both 2- and 3-thiols can be obtained by reaction of lithiated furans with sulfur in each case the predominant tautomer is the thiol form. ... 

Winslow et investigated the use of tetracarbethoxyfuran as a diene, and as expected it does not react with maleic anhydride. However, the tetra alcohol, which can be obtained by the LiAlH4 reduction, reacts easily. From the point of view of preparative utility, alkoxy- and acetoxyfurans are valuable as dienes. They have recently been obtained relatively easily from 2,5-dialkoxy- or 2,5-diacetoxy-dihydrofurans. The normal products with maleic anhydride, maleim-ide, fumaronitrile, and dimethylacetylene dicarboxylate have been described. The stereochemistry of the products was not... 

Pyridazine itself is best prepared (in about 60-67% yield) from 2,5-diacetoxy- or 2,5-dimethoxy-2,5-dihydrofuran (50ACS1233, 56JOC764) or by hydrodehalogenation of 3-chloro-... 

The conversion of furans by oxidative acetylation or methoxylation to 2,5-diacetoxy- or 2,5-dimethoxy-2,5-dihydrofurans respectively, and their subsequent hydrogenation to the corresponding tetrahydrofurans, provides a useful source of protected 1,4-dicarbonyl compounds capable of conversion inter alia into the other five-membered heterocycles [Pg.142]

The reaction of furan with benzoyl peroxide gave in good yield the cis- and sodium acetate in the presence of furan gave 2,5-diacetoxy-... 

The most important derivatives of 2,5-dihydrofuran are the 2,5-dialkoxy and 2,5-diacetoxy compounds which are easily prepared from furans (Section 3.11.2.3). Their vast utility is as synthetic equivalents of malealdehyde and its derivatives (60MI31100). Suitable intermediates for Robinson-Schopf synthesis have been obtained in this way. Pyridazines are readily obtained (Scheme 121), and 3-pyridinols are available from 2-furylmethanamines (Scheme 122). This approach has been used in a synthesis of pyridoxine. The 2,5-diacetoxy... 

Via Elimination of A kohol or W alter from Dihydrofurans Pyrolysis of 2,5-dialkoxy- or -diacetoxy-2,5-dihydrofurans results in a smooth reaction with the formation of 2-substituted furans.39 40... 

The presence of halide ions in the anolyte may efficiently help the oxidative addition of the solvent to an unsaturated compound the addition may be followed by a bond cleavage [164]. The conversion of furan into either 2,5-dimethoxy-2,5-dihydrofuran [165,166] or 2,5-diacetoxy-2,5-dhydrofuran [167] has been shown to be possible in methanol or an acetic acid-acetonitrile mixture, respectively (Scheme 24). 

The reaction of several a-diazoketones with ethyl vinyl ether under various conditions has been examined. In the presence of metal salts [Rh2(OAc)4, Pd(OAc)2, CuCl] ethoxy dihydrofurans are produced. The initial product of this reaction sequence is a cyclopropyl ketone which suffers from a spontaneous rearrangement to the dihydrofuran <96CJC2401>. An efficient synthesis of 3-acylfurans is achieved by Ag(I)/Celite mediated cycloaddition of dicarbonyl compounds with vinyl sulfide (<97TL5671> see also <97TL2095>). A two-step synthesis of 2-substituted 4-furanmethanol compounds was reported. The method involves a Homer-Wadsworth-Emmons reaction between 3-ketophosphonates and l,3-diacetoxy-2-... 

Enyne metathesis/metallotropic [l,3]-shift domino processes are also valuable for natural product synthesis [33c,d]. Reaction of substrate 168 with cis-l,4-diacetoxy-2-butene in the presence of Grubbs catalyst 2 generated the intermediate ruthenium alkinyl carbene through a relay RCM with the hberation of 2,5-dihydrofuran followed by metallotropic [l,3]-shift and terminating (Z)-selective CM with the co-olefin to yield the conjugated enediyne 169 (Scheme 2.58) [33c]. The antitumor active Panax ginseng constituent (3R,9R,10R)-panaxytriol was readily synthesized from 169 in six steps. 

Ethoxy-4-nethyloxazole reacts similarly with a variety of ethers and esters of 2-butene-l,4-diol. ° l,4-Dimethoxy-2-butene forms XII-286 (R = CH3) 2,5-dihydrofuran forms the p5oidoxine cyclic ether (MI-289) ° and 1,4-diacetoxy-2-butene forms pyridoxine. ... 

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