Tetrahydrofuran ring opening

If R3 or R4 is a 2-hydroxyethyl group or a 2-acetoxyethyl group, treatment with hydrochloric acid yield 3-(2-methyl-4-amino-5-pyrimidi-nylmethyl)-2,3,3a,5,6,6a-hexahydrofuro[2,3-d]thiazole-2-thione (CXCVI) with liberation of water or acetic acid (Table 21). On further hydrolysis with acids the tetrahydrofuran ring opens again and 3-(2-methyl-4-amino-5-pyrimidinylmethyl)-4-methyl-5-(2-hydroxyethyl)-/l4-thiazoline-2-thiones are obtained (Table 29)-... 

The 3-thioxo-furo[2,3-fif iniidazol-6-yl acyclo C-nucleosides 101 undergo facile acid-catalyzed tetrahydrofuran ring opening to give the imidazol-4-yl acyclo C-nucleosides 100 (84MI11 88MI8) and 5-benzylation to 102 (84MI6) (Scheme 31). 

Without additional reagents lyl-Alkoxyhalides from oxo eompounds s. U, 908 Halogenhydrins from oxido compounds s. A, 475 s. a. J. L. Bose, A. B. Foster, and R. W. Stephens, Soc. 1959, 3314 Reactions with carbamyl chloride Chlorourethans s. 11, 590 Chloroallophanates from allophanyl chloride s. 11, 591 Oxetane ring opening lodohydrins from cyclic ethers s. 12, 626 Tetrahydrofuran ring opening s. 11, 1 w.a.r. CO C(OR)Hal C C -> C(OH)CHal... 

Uses. Furfural is primarily a chemical feedstock for a number of monomeric compounds and resins. One route produces furan by decarbonylation. Tetrahydrofuran is derived from furan by hydrogenation. Polytetramethylene ether glycol [25190-06-1] is manufactured from tetrahydrofuran by a ring opening polymeri2ation reaction. Another route (hydrogenation) produces furfuryl alcohol, tetrahydrofurfuryl alcohol, 2-methylfuran, and 2-methyltetrahydrofuran. A variety of proprietary synthetic resins are manufactured from furfural and/or furfuryl alcohol. Other... 

Cyclic ether and acetal polymerizations are also important commercially. Polymerization of tetrahydrofuran is used to produce polyether diol, and polyoxymethylene, an excellent engineering plastic, is obtained by the ring-opening polymerization of trioxane with a small amount of cycHc ether or acetal comonomer to prevent depolymerization (see Acetal resins Polyethers, tetrahydrofuran). 

The polymerizations of tetrahydrofuran [1693-74-9] (THF) and of oxetane [503-30-0] (OX) are classic examples of cationic ring-opening polymerizations. Under ideal conditions, the polymerization of the five-membered tetrahydrofuran ring is a reversible equiUbtium polymerization, whereas the polymerization of the strained four-membered oxetane ring is irreversible (1,2). 

Because of the high ring strain of the four-membered ring, even substituted oxetanes polymerize readily, ia contrast to substituted tetrahydrofurans, which have tittle tendency to undergo ring-opening homopolymerization (5). 

Cationic ring-opening polymerization is the only polymerization mechanism available to tetrahydrofuran (5,6,8). The propagating species is a tertiary oxonium ion associated with a negatively charged counterion ... 

The parallel ability of oxiranes to undergo ring opening to carbonyl ylides was first noted in the case of tetracyanooxirane (68T2551), but such reactions have not been widely exploited. The addition to alkenes, leading to formation of tetrahydrofurans, is stereospecific (Scheme... 

Reductive ring opening of the [i-lactam 10 (X = O), obtained by [2 + 2] cycloaddition of chloro-sulfonyl isocyanate and tetraphenylcyclopentadiene followed by treatment with /7-cresol, with sodium hydride in anhydrous tetrahydrofuran yields 3,5,6,7-tetraphenyl-2//-azepin-2-one (11, X = O).41 Surprisingly, similar treatment of the reduced /Mactam 10 (X = H2) is reported to yield 3,5,6,7-letraphenyl-2//-azepine (11, X = H2), the first monocyclic 277-azepine to be isolated and characterized. Physical data for this compound, however, are inconclusive and attempts to reproduce this synthesis have failed.291... 

There are two possible ways for the ring opening of 35 in the polymerization The C1—O7 bond cleavage leads to the formation of a substituted tetrahydropyran ring 36 in the polymer chain, while the C1—O2 bond cleavage produces a substituted tetrahydrofuran ring 37. Product analysis of the acid-catalyzed hydrolysis of the... 

Although it is unlikely that the tetrahydrofuran ring would open under these conditions of polymerization, the polymer was hydrolyzed in 0.2 M sodium hydroxide solution, in order to confirm its structure. Clear colorless liquid was obtained after acidification followed by esterification with diazomethane. Its IR and NMR data compares exactly to that obtained from 59 which was prepared from the neutral hydrolysis of 57 and esterification of the resultant acid with diazomethane. Since the apparent sole product obtained from hydrolysis of the polymer was 59, they conclude that 58 represents the correct structure for this polymer. 

Polytetramethyleneglycol (polytetrahydrofuran) is formed by ring opening polyetherification of tetrahydrofuran. Branched polyalkyleneoxides are formed using polyfunctional alcohols such as trimethylolpropane and pentaerythrite. The products are liquids or waxes depending on the molar mass. Polyalkyleneoxides are often precursors for demulsifiers. 

This article aims to review papers that were published in 2006 on reactions and syntheses of furans, benzofurans and their derivatives. Two reviews have summarized the syntheses of furans <06OBC1627> and tetrahydrofurans <06EJO1627>. Another review <06001613> records the progress of transition metal-catalyzed asymmetric ring opening of oxabenzonorbornadienes. 

Reaction of 4a-c with hydrogen chloride was carried out at room temperature in various solvents including dichloromethane, diethyl ether, tetrahydrofuran, acetonitrile, DMF, and l,l,l,3,3,3-hexafluoropropan-2-ol (HFIP). The ring opening of 4a-c readily proceeded to give the ester 10 as well as chloride substitution products, 8K and 9K, as shown in Scheme 8 (9). Product yields are dependent on the solvent, as summarized in Table II. Ester 10... 

The compound 5-[5-(4-chlorophenyl)furan-2-yl]-2,3,4,5-tetrahydrofuran-2-one (F-1044, 7.85) is a nonsteroidal anti-inflammatory agent possibly acting via a ring-opened hydroxybutyric acid metabolite. To examine this hypothesis, F-1044 was submitted to extensive in vivo testing, which revealed potent activities and a unique pharmacological profile markedly different from that of acidic nonsteroidal anti-inflammatory drugs [169], These results have been interpreted to mean that part or most of the observed effects of F-... 

In contrast to the relative chemical stability of mono-epoxides, diol epoxides of fatty acids (10.52), which are formed from di-epoxides by EH, are subject to a different fate. In such metabolites, intramolecular nucleophilic substitution may occur, such that oxirane opening is accompanied by formation of a tetrahydrofuran ring [134], Such reactions of intramolecular nucleophilic substitution are discussed in detail in Sect. 11.9. In the case of diol epoxides of fatty acids, the resulting tetrahydrofuran-diols (10.53) are part of a much larger ensemble of oxygenated metabolites of fatty acids, the potential cytotoxicities of which are being evaluated [135]. 

The cationic ring-opening polymerization of epichlorohydrin in conjunction with a glycol or water as a modifier produced hydroxyl-terminated epichlorohydrin (HTE) liquid polymers (1-2). Hydroxyl-terminated polyethers of other alkylene oxides (3 4), oxetane and its derivatives (5 6), and copolymers of tetrahydrofuran (7-15) have also been reported. These hydroxyl-terminated polyethers are theoretically difunctional and used as reactive prepolymers. 

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