Furan catalytic reduction

Dihydrobenzo[c]furan-4,7-diones (e.g., (Ill)) can be converted to benzo[c]furans. Catalytic reduction of (111) and treatment of the resulting product with phenyllithium yields a diol (112), which can be dehydrated to (113) (Scheme 85) <73BSF1154>. 

Alteration of the structural pattern produces a pair of adrenergic a-blocking agents which serve as anti hypertensives. These structures are reminiscent of prazoci n. Reaction of piperazine with 2-furoy1 chloride followed by catalytic reduction of the furan ring leads to synthon 69. This, when heated... 

These results mark the very first successful catalytic reduction of furans in high enantioselectivity and greatly expand the methods available for the synthesis of enantiopure heterocycles. 

A Furan enters into a cycloaddition reaction with the dienophile diethyl acetylcnedicarboxylate to form an adduct. Catalytic reduction occurs preferentially at the more electron-rich double bond of the adduct, and the dihydro product, upon heating, undergoes a reverse Diels-Alder reaction to release ethene and the diesier (Scheme 6.29),... 

Catalytic reduction of pyrroles gives successively A3-pyrroles and pyrrolidines. Tetrahydrofurans are formed by the catalytic reduction of furans with Raney nickel and hydrogen ring cleavage products... 

Tetrahydrofuran is a commonly used solvent. It is a relatively stable ether and is miscible with both water and organic solvents. It is manufactured on a large scale by dehydration of butane-1,4-diol and catalytic reduction of furan. It is also obtained by base treatment of 4-haloalkan-l-ols and by acidic treatment of alk-3-en-l-ols and alk-4-en-l-ols. 

The (aminomethyl)thiophene-2-carboxylic acid isomers were prepared from the corresponding methylthiophene-2-carboxylic acid esters, as exemplified for the 3-(aminomethyl) isomer 79 (Scheme 22))66 The 4-(aminomethyl) isomer was prepared in the same way, but with a low yield for the bromination step (7%))66,111 For the 5-(aminomethyl) isomer the bromomethyl compound was reacted with sodium azide, followed by catalytic reduction)74 The corresponding furan and pyridine analogues were prepared similarly. 

Dihydrobenzo[ furan is reductively cleaved by treatment with hydrosilanes in the presence of catalytic amounts ofB(G6Fs)3 in high yield giving 2-phenylethanol <2000JOC6179>. l,3-Dihydrobenzo[c]furan is cleaved to the lithium alkoxide of 2-hydroxymethylphenylmethyllithium, which can be usefully trapped with electrophiles <2004S1115>. 

Both 2- and 3-nitrothiophenes are reduced by tin and hydrochloric acid to the corresponding aminothiophenes. Reduction of 2,5-dibromo-3,4-dinitrothiophene gives 3,4-diaminothiophene as a stable crystalline solid. 2-Acetamido-furans are prepared by the reduction of 2-nitrofurans in the presence of acetic anhydride. 2-Substituted 5-nitrofurans can be reduced to the S-aminofurans by an electrochemical method. Although catalytic reduction gives 2-aminofurans only in low yields, they can be trapped using ethyl ethoxymethylenecyanoacetate or ethoxymethylenemalononitrile. Benzofuranone 412 and not 2-aminobenzofuran is obtained from tin and hydrochloric acid treatment of 2-nitrobenzo[ ] furan 411. 

As in all catalytic reductions, the purity of the starting material is of great importance. Redistilled furan, b.p. 31-32 , prepared by the method of Wilson (Org. Syn. Coll. Vol. i, 269) is quite satisfactory. It has been reported that furan prepared by the method of Gilman and Louisinian should be dried over calcium chloride and fractionated carefully. It is advisable to redistil the furan shortly before use and to avoid contact with rubber stoppers. 

The parent 2-aminofuran 103 is extremely unstable but when generated in situ, by catalytic reduction of 2-nitrofuran, and immediately reacted with the electrophiles ethoxymethylene malononitrile (EMMN) and ethyl ethoxymethylenecyanoacetate (EMCA) the 5-substitution products 104 were formed in low yield (Eq. (16)) (93JHC113). If the 5-position is blocked as in the case of the 5-methyl derivative 105, or 2-aminobenzo[Z>]furan, then substitution occurs at position 3, e.g. 106 (Eq. (17)) (93JHC113). 

Nakagawa Y, Tamura M, Tomishige K (2013) Catalytic reduction of biomass-derived furanic compounds with hydrogen. ACS Catal 3 2655-2668... 

F and MF are typical precursors to furan monomers bearing a moiety which can be polymerized by chain-reaction mechanisms. Scheme 6.11 provides a non-exhaustive array of entries into such structures, which have all been synthesized, characterized and polymerized [4], A major exception to this general postulate is constituted by furfuryl alcohol (2-hydroxymethylfuran, FA), which is in fact still today the most important commercially available furan compound, obtained by the catalytic reduction of F involving more than 80 per cent of its world production. FA is widely used as a polycondensation monomer and does not therefore belong to the class of coirpounds shown in Scheme 6.11. 

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