Furans furan ethers

Fig (19) Octalin ketal (163) is converted to kete dithioacetal (164) by the cleavage of ketal function and condensation with carbon disulfide and methyl iodide. Subjection of (164) to the action of dimethylsulfonium niethylide and acid hydrolysis leads to the formation of unsaturated lactone (165).lts furan silyl ether derivative is caused to undergo Diets-Atder reaction with methyl acrylate to obtain salicyctic ester (166) which is converted by standard organic reactions toabietane ether (167). It is converted to aiiylic alcohol (168) by epoxidation and elimination. Alcohol (169) obtained from (168) yields orthoamide which undergoes transformation to amide (170). Its conversion to the previously reported intermediate has been achieved by epoxidation, elimination and hydrolysis. 

Choo 1993 Furan, vinyl ether Allinger 1993b... 

Main components In the fresh herb 0.5-1.5%, in the dried herb 0.05-0.35% essential oil, which contains up to 40% a-phellandrene, as well as limonene, carvone, and dill furan (dill ether, 3,8-epoxy-p-menth-l-en) as main components [86, 87, 88]. The latter should be present in a minimum of 5% as an indicator of pure herb oil ]89, 90]. 

A 1,3-dibromo ketone was also reductively cyclized with lithium dimethylcuprate in diethyl ether, containing furan, to form tetramethylcyclopropanone by a two-electron reduction and subsequent addition of the cuprate across the reactive carbonyl function to give 34. Side products include 2,2,4-trimethylpentan-3-one and the [3-f4] cycloaddition product of the cyclopropanone with furan. An ethereal medium is a requirement, since the same reaction in pentane at — 50°C did not lead to cyclopropane derivatives. More detailed information on the in situ generation of cyclopropanenes and subsequent addition of nucleophiles is given in Section 1.1.3.3. 

On the contrary, encapsulation of the larger K" " or NH4 ions should lead to the formation of metallacrown ether sandwich complexes (M+ MC= 1 2). Reaction of diethyl ketipinate H2L 13 with copper(ll) acetate in the presence of calcium nitrate affords green microcrystals 14 after crystallization from tetrahydro-furan/diethyl ether (Scheme 1). 

In this second case the reaction proceeds through an electron transfer mechanism. Monomers having nucleophilic features, such as ethyleneimine, furan, some ethers, react following scheme a). Other monomers, with no basic groups in their molecule, as styrene MeSt, Cp, undergo the electron transfer reaction. 

Furan, 2,2 -[oxybis(methylene)lbis-, 2,2 -(oxydimethylene)his(furan), 2-[(2-furylmethoxy) methyljfuran, 2-[(furfuryloxyjmethyl]furan, difurfuryl ether [4437-22-3] FEMA 3337... 

Following a series of exposures, the films were extracted successively with methanol and methylene chloride. Portions of these extracts were evaporated to dryness and the residues were taken up in 1 1 tetrahydro-furan-diethyl ether for delayed emission determinations at 77K. Emission spectra were measured in an Aminco-Bowman Spectrophosphorimeter fitted with a -P28 photomultiplier the spectra are uncorrected for instrument response. 

Dimethoxyfuran reacts with dienophiies such as dimethylmaleic anhydride under high pressure 99 methylenecyclobutenone and cyciobutenedione (giving (95)) react straightforwardly. 0 The furan-derived ether (96a> fails to... 

Cottier L, Descotes G, Soro Y (2003) Heteromacrocycles from ring-closing metathesis of unsaturated furanic ethers. Synth Commun 33 4285 295... 

Fig. 11 Side products in the sucrose-to-lactate (green) convta ion in MeOH and their raigin blue retro-aldol of glucose (see Sect. 7) red methanolysis of sucrose ot acetalizatirai of glucose black dehydration of sugars to HMF, furan ethers and humins. MMHB methyl methoxy-2-hydroxybutanoate, MVG methyl vinyl glycolate, MHB methyl-2-hydroxybutanoate, GADMA glycolaldehyde dimethyl acetal. HG = hydrogenation...

Although early attempts were unsuccessful, it is possible to reduce 7V-methyl-2-pyridones with lithimn aluminum hydride and aluminum chloride in tetrahydro-furan or ether, or without aluminum chloride in tetrahydrofuran. N-Methyl-2-pyridone (MI-640, R = H) gives l-methyl-3-piperideine (XII-641, R = H) as the major product and 1,4-dimethyl-2-pyridone (XD-640, R = CH3) gives... 

The toxic effects of PCP are due not only to the undissociated PCP but also to other impurities, such as the polyehlorinated dioxins, furans, and ethers (Ahlborg and Thunberg, 1980 Rao, 1978). PCP formulations in oil are therefore more toxic than in aqueous media. 

The intramolecular cyclization of a stabilized phosphonate carbanion onto an aldehyde has proved to be an effective method for the synthesis of brefeldin polyene macrolides, and in a formal synthesis of carbomycin Pyrenophorin has been synthesized using a pent-3-enoic acid d reagent two other routes to the racemic compound have also appeared. Macrocyclic polyether macrolides have been prepared by cyclization, and by ozonolysis of a furan crown-ether compound. 

Dibromodiphenylamine treated with 1 equivalent of an ethereal soln. of methyllithium under Ng followed by a soln. of diethyl sulfate in tetrahydro-furan, the ether removed by distillation, then refluxed 15 hrs. N-ethyl-2,2 -dibromodiphenylamine. Y 83%. H. Gilman and E. A. Zuech, Ghem. and Ind. 1958, 1227 Am. Soc. 82, 2522 (1960). 

Octaphenylcyclotetrasilane is cleaved by phenyllithium in a tetrahydro-furan-ether mixed solvent system. When equimolar quantities of the reactants are stirred for 5 hours, 55% of the octaphenylcyclotetrasilane is recovered and decaphenylcyclopentasilane is obtained in 18% yield. 

Methyllithium also cleaves octaphenylcyclotetrasilane in a tetrahydro-furan-ether solvent. Two equivalents of methyllithium brii about cleavage within 30 minutes to give l-lithio-4-methyloctaphenyltetrasilane in yields up to 66%, as indicated by derivative formation using trimethyl phosphate to obtain 1,4-dimethyloctaphenyltetrasilane (34). Acid hydrolysis of the reaction mixture leads to lff-4-methyloctaphenyltetrasilane (42) in comparable yield. The use of a loiter reaction time and a large excess of methyllithium leads to lH-2-methyltetraphenyldisilane (43) as the major product (65%), after acid hydrolysis. ... 

Phenyllithium slowly cleaves decaphenylcyclopentasilane in tetrahydro-furan-ether to give, with an excess of organometallic compound and extended reaction times, pentaphenyldisilane (45) as the major product after acid hydrolysis. Decaphenylcyclopentasilane reacts with a 5 mole excess of methyllithium to give l-lithio-2-methyltetraphenyldisilane, characterized as 1,2-dimethyltetraphenyldisilane (23). ... 

The oxidation of the cyclic enol ether 93 in MeOH affords the methyl ester 95 by hydrolysis of the ketene acetal 94 formed initially by regioselective attack of the methoxy group at the anomeric carbon, rather than the a-alkoxy ketone[35]. Similarly, the double bond of the furan part in khellin (96) is converted ino the ester 98 via the ketene acetal 97[l23],... 

The 7, i5-unsaturated alcohol 99 is cyclized to 2-vinyl-5-phenyltetrahydro-furan (100) by exo cyclization in aqueous alcohol[124]. On the other hand, the dihydropyran 101 is formed by endo cyclization from a 7, (5-unsaturated alcohol substituted by two methyl groups at the i5-position. The direction of elimination of /3-hydrogen to give either enol ethers or allylic ethers can be controlled by using DMSO as a solvent and utilized in the synthesis of the tetronomycin precursor 102[125], The oxidation of the optically active 3-alkene-l,2-diol 103 affords the 2,5-dihydrofuran 104 in high ee. It should be noted that /3-OH is eliminated rather than /3-H at the end of the reac-tion[126]. 

The cyclic enol ether 255 from the functionalized 3-alkynoI 254 was converted into the furans 256 by the reaction of allyl chloride, and 257 by elimination of MeOH[132], The alkynes 258 and 260, which have two hydroxy groups at suitable positions, are converted into the cyclic acetals 259 and 261. Carcogran and frontalin have been prepared by this reaction[124]. 

The furan nucleus is a cycHc, dienic ether with some aromaticity (2). It is the least aromatic of the common 5-membered heterocycles. A comparison of the aromaticity (3) of several of these compounds is shown below. 

Alkylfurans, halofurans, alkoxyfurans, furfuryl ester and ethers, and furfural diacetate [613-75-2] behave similarly. Furans containing electron withdrawing constituents, for example, furfural, 2-furoic acid, and nitrofurans, fail as dienes even with very strong dienophiles. 

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