Furan hydration

Aqueous mineral acids react with BF to yield the hydrates of BF or the hydroxyfluoroboric acids, fluoroboric acid, or boric acid. Solution in aqueous alkali gives the soluble salts of the hydroxyfluoroboric acids, fluoroboric acids, or boric acid. Boron trifluoride, slightly soluble in many organic solvents including saturated hydrocarbons (qv), halogenated hydrocarbons, and aromatic compounds, easily polymerizes unsaturated compounds such as butylenes (qv), styrene (qv), or vinyl esters, as well as easily cleaved cycHc molecules such as tetrahydrofuran (see Furan derivatives). Other molecules containing electron-donating atoms such as O, S, N, P, etc, eg, alcohols, acids, amines, phosphines, and ethers, may dissolve BF to produce soluble adducts. 

The Diels-Alder adduct, anhydride 63, on treatment with hydrazine hydrate in acetic acid for 20 min yielded 252 which on keeping in acetic acid for further 8 h gave the imide derivative 253. This adduct, imide 253, underwent retro-Diels-Alder reaction to eliminate furan giving amino maleimide derivative 254 (Scheme 45) <2005J OC4553>. 

Phomactin A is the most challenging family member architecturally. The fragments that are most challenging are highlighted in Fig. 8.4. In Box-A, the highly sensitive hydrated furan is prone to dehydration under acidic or basic conditions, and any total synthesis almost certainly must save introduction of this fragment until the end game. Box-B relates to the strained and somewhat twisted electron-rich double bond. This trisubstituted olefin is extremely reactive toward electrophilic oxidants. 

We had two possible routes in which alcohol 72 could be used (Scheme 8.19). Route A would involve rearrangement of tertiary alcohol 72 to enone 76. Deprotonation at C5 and generation of the enolate followed by exposure to an oxaziridine or other oxygen electrophile equivalents might directly afford the hydrated furan C-ring of phomactin A (see 82) via hydroxy enone 81. We had also hoped to make use of a chromium-mediated oxidative rearrangement of tertiary allylic alcohols. Unfortunately, treatment of 72 to PCC produced only unidentified baseline materials, thereby quickly eliminating this route. 

The hydrated furan-2-carboxylate, Np02(C4H30C02)-2H20, and the thiophene-2-carboxylate, Np02(C4H3SC02)-2H20, dehydrate at 90 °C and 100 °C respectively it is possible that the ring O and S atoms in these two carboxylates are also bonded to the metal atom. 

Somewhat more complex is the reaction described by Boeseken.1- whereby diallyl can bo converted into 2,5-diacetoxvmethyltetm.hyrlr 11 -furan on treatment with peracetic acid (Eq. 748). This transformation was presumed to occur by way of I. 2 5,6-diepoxy hexane, which reacts further with acetic acid present in the oxidizing solution. Ross1481 h i observed a similar cydization while attempting acid-catalyzed hydration of authentic 1,2 5,C-diepoxyhexane. 

Other attempts to avoid the experimental difficulties of measuring the thermal properties of gas hydrates have been to choose the easier route of thermal property measurements of cyclic ethers-ethylene oxide (EO) for structure I, or tetrahydro-furan (THF) for structure II. Since both compounds are totally miscible with water, liquid solutions can be made at the theoretical hydrate compositions (EO 7.67H20 or THF 17H20). 

Poly([7,8-bis(trifluoromethyl)tetracyclo [4.2.0.02 8.05 7]octane-3,4-diyl]-1,2-ethenediyl), 3457 Poly[borane(l)], 0134 crs-Poly (butadiene), 1480 Poly(l,3-butadiene peroxide), 1528 Poly(butadiyne), 1382 Poly(carbon monofluoride), 0336 Poly(chlorotrifluoroethylene), 0589 Poly(l,3-cyclohexadiene peroxide), 2380 Poly(cyclopentadienyltitanium dichloride), 1837 Poly(diazidophosphazene), 4781 Poly(dibromosilylene), 0282 Poly(difluorosilylene), 4324 Poly(dihydroxydioxodisilane), 4474 Poly(dimercuryimmonium acetylide), 0665 Poly(dimercuryimmonium azide), 4606 Poly(dimercuryimmonium bromate), 0253 Poly (dimercury immonium iodide hydrate), 4449 Poly (dimercury immonium perchlorate), 4006 Poly(dimercuryimmonium permanganate), 4603 Poly (dime thylketene peroxide), see Poly(peroxyisobutyrolactone), 1531 Poly(dimethylsiloxane), 0918 Poly(disilicon nitride), 4752 Poly(ethenyl nitrate), see Poly(vinyl nitrate), 0760 Poly(ethylene), 0778 Poly(ethylene terephthalate), 3256 Poly(ethylidene peroxide), 0831 Poly(furan-2,5-diyl), 1398 Poly(germanium dihydride), 4409 Poly(germanium monohydride), 4407 Poly(isobutene), 1578 Poly(methyl methacrylate peroxide), 1913... 

Hydration or elimination of glycals. Glycals can undergo hydration or elimination when treated with HgS04 in dilute sulfuric acid or aqueous acetic acid.1 However, D-glucal 1 is converted only into the (l,2-dihydroxyethyl)furan (2).2 This product has been used for a short synthesis of L-hexoses. Thus 2 can be converted to the monobenzoate 3 with inversion (Mitsunobu). This product is converted into... 

In vitro ICL50, ICT50, and in vivo antitumour activities have been determined for the platinum(II) and palladium(II) complexes (418) and (419) of l,6-diaminotetrahydropyrrolo[2,3-5]pyrrole-2,5(1 i/,4/f)-dione (417) <89JCR(M)63i). Compound (417) can be obtained in 63% yield by slow addition ofhexahydrofuro[2,3-6]furan-2,5-dione (416) to boiling 80% hydrazine hydrate <93CB2159>. 

As demonstrated below, a Lewis acid-mediated reaction was utilized in the synthesis of dihydro[b furan-based chromen-2-one derivatives from l-cyclopropyl-2-arylethanones and allenic esters <070L4017>. The TiCh-catalyzed anti-Markovnikov hydration of alkynes, followed by a copper-catalyzed O-arylation was applied to the synthesis of 2-substituted benzo[6]furan <07JOC6149>. In addition, benzo[6]furan-based heterocycles could be made from chloromethylcoumarins <07SL1951>, substituted cyclopropanes <07AGE1726>, as well as benzyne and styrene oxide <07SL1308>. On the other hand, DBU-mediated dehydroiodination of 2-iodomethyl-2,3-dihydrobenzo[6]furans was also useful in the synthesis of 2-methylbenzo[Z>]furans <07TL6628>. 

Iron complexes with hydrated furane ligands are available from appropriate alkynyl- and alkenyl-substituted iron compounds as precursors 174). 

A Ni-catalyzed cyclization cross-coupling reaction of iodoalkenes with alkyl zinc halides has been employed for the synthesis of various tetrahydrofuran derivatives <2007AGE-ASAP>. The TiCU-catalyzed anti-Markovnikov hydration of alkynes has been applied to the synthesis of various benzo[3]furans <2007JOC6149>. 

Reactions in bcnzonitrilc give the corresponding bis(trifluoromethylated) diketones 25 cyclic diols. based on saturated furan or pyran rings, are also formed by intramolecular nucleophilic cyclization of hydrated forms. 

Furan derivatives are formed when aqueous solutions of amines react with diacetylenic alcohols and glycols. Thus when 155 is heated with aqueous dimethyl-amine, the aminofuran 158 is formed . The initial steps involve amine addition and hydration giving 156 which suffers dealdolization to give the ketone 157. In the case of tertiary glycols such as 159, a similar sequence of steps followed by hydrolysis of the intermediate enamine produces the furanone 160 . ... 

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