Furans reactions

When undiluted 2-vinylfuran was added to metallic sodium (mirror or particles) an orange colour developed and some resinous material was deposited on the metal surface. On prolonged contact much of the monomer was converted into a partly-insoluble reddish resin with spectra unrelated to those of standard poly(2-vinyl-furan). Reaction of diluted monomer with sodium gave a milder interaction, but no evidence of living anionic polymerization. 

Furan, reaction with bromine and methanol to yield 2,5-dimethoxy-2,5-dihydrofuran, 40, 29 Fuean, 2,5-DmYDRO-2,5-dim-ethoxy-, 40, 29... 

It has been found that furans undergo hydrogenolyses under very mild conditions. Such conditions are too mild to hydrogenolyze oxolanes (saturated furans). As concerns regioselectivity, the furan C-O bond rupture takes place in the sterically less hindered position, similar to the reaction in the oxolanes. The oxacycloalkene intermediate of an intramolecular Diels-Alder furan reaction was hydrogenolized over Pd/BaS04.27... 

Furans. Reaction of a,a-dimethoxy ketones with 1 affords a dihydrofuran (2) presumably via a carbene (a) that inserts intramolecularly into a C—H of an adjacent methoxy group. The reaction often results directly in a furan, since the elimination of methanol from 2 is facile. 

Regioselective [3 + 2] annulation has been reported for the preparation of a wide variety of furans. Reaction of acid chlorides with trialkylsilyl-substituted allenes under the influence of A1C13 (CH2C12, — 20°C) yields the desired compounds (Scheme 52). The intramolecular variant of this method has also been described (89JA4407). 

Condensation of 1,2-dielectrophiles with a component that serves as a l,3-C,0-nucleophile is the underlying principle of a number of improved methods for furan synthesis. Bis-silyl enol ethers are suitable enol equivalents for the condensation with dielectrophiles to produce furans. Langer and co-workers have made use of this concept in the synthesis of annulated furans with l-chloro-2,2-dimethoxyethane as electrophile <2005EJ02074>. In a stepwise reaction comprising TMS triflate-assisted aldol reaction and cyclization with l,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as a base, 3-methoxy exomethylene tetrahydrofurans are obtained, which finally yield the furan reaction products upon treatment with trifluoroacetic acid (Scheme 18). 

That product (17) is then converted to the activated A -hydoxysuccinimide derivative 18 as in the case of the monocyclic furan. Reaction with the primary amine 10 used to prepare amprenavir then leads to the urethane (19). Reduction of the nitro group then affords darunavir" (20). 

Entry Oxyallyl Cation Furan Reaction Conditions Oxabicydic Product Ref... 

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