Furan-2-carbaldehyde

Hydroxypropyl)-7-methoxy-2-(3 -methoxy-4 -hydroxyphenyl)-3-benzo[b]furan-carbaldehyde (benzofuran)... 

Figure 10.7 Tautomeric imines of o-hydroxybenzo[6]furan carbaldehydes.

Although the same theoretical studies indicate very small energy differences between the syn and anti conformers of the 3-carbaldehydes of furan, thiophene and pyrrole with a slight preference for the syn conformer, in chloroform solution the furan- and thiophene-3-carbaldehydes adopt the anti conformers to the extent of 100 and 80% respectively (82X3245). However, A-substituted 3-(trifluoroacetyl)pyrroles exist in solution as mixtures of rotational isomers (80JCR(S)42). 

The carbonyl reactivity of pyrrole-, furan-, thiophene- and selenophene-2- and -3-carbaldehydes is very similar to that of benzaldehyde. A quantitative study of the reaction of iV-methylpyrrole-2-carbaldehyde, furan-2-carbaldehyde and thiophene-2-carbaldehyde with hydroxide ions showed that the difference in reactivity between furan- and thiophene-2-carbaldehydes was small but that both of these aldehydes were considerably more reactive... 

Benzo[c]furan, 1,3-dihydro-1 -phenyl- H NMR, 4, 574 <75JA5160> Benzo[b]furan-2-carbaldehyde, 3,6-dimethoxy-UV, 4, 589 <71AJC1883> Benzo[b]furan-2-carbaldehyde, 3-methoxy-UV, 4, 589 <73AJC1079>... 

H NMR, 4, 558 <65ACS485) Furan-2-carbaldehyde (furfural) dipole moment, 4, 555 (B-63MI31000, 65MI31001) AHe, 4, 543 (72T3015)... 

UV. 4, 14 <71PMH(3)79), 588 (50JA753) Furan-2-carbaldehyde, trans-2-acetoxy-5-nitro-2,5-dihydro-, diacetate X-ray, 4, 549 (80T1817)... 

Furan-2-carbaldehyde, 5-hydroxymethyl- C NMR. 4, 565 <76AJC107) Furan-2-carbaldehyde, 3-methoxy-... 

H NMR, 5, 558 <71BSF990) Furan-2-carbaldehyde, 4-methoxy- H NMR, 4, 558 <7IBSF990) Furan-2-carbaldehyde, 5-methyl- C NMR, 4, 565 (76AJCI07) Furan-2-carbaldehyde, 5-nitro-UV, 4, 588 <50JA753)... 

Furan-2-carbaldehyde, 5-trifluoromethyl- H NMR, 4, 558 (68JHC95) Furan-2-carbaldehyde oxime, 5-nitro-X-ray, 4, 537 (72JCS(P2)I033) Furan-3-carbaldehyde... 

Furan-2-carbaldehyde, 3-amino-Friedlander synthesis, 4, 648 Furan-2-carbaldehyde, 3-azido-reduction, 4, 647 Furan-2-carbaldehyde, 4-bromo-X-ray diffraction, 4, 543 Furan-2-carbaldehyde, 5-bromo-nucleophilic substitution, 4, 612 reactions... 

Furan-2-carbaldehyde, 5-methyl-synthesis, 4, 658 Furan-2-carbaldehyde, 5-nitro-as chemotherapeutic agent, 1, 179... 

Liquid-phase photolysis of furan atroom temperature occurred in very low yields (1 % conversion), giving a mixture of Diels-Alder adducts deriving from the reaction of cyclopropene-3-carbaldehyde and formylallene with furan (85JOC3034). 

Due to the /( -elimination of thiolate, the enolate of (2/ ,5/ )-2-/enolate formed in situ delivers the adducts in >90% diastereoselectivity and about 50% chemical yield115. 

However, considerable amounts of 2,3-dihydrofuran 50 and tetrahydro-furan-2-carbaldehyde 53 were present because of an isomerization process. The isomerization takes place simultaneously with the hydroformylation reaction. When the 2,5-dihydrofuran 46 reacts with the rhodium hydride complex, the 3-alkyl intermediate 48 is formed. This can evolve to the 2,3-dihydrofuran 50 via /3-hydride elimination reaction. This new substrate can also give both 2- and 3-alkyl intermediates 52 and 48, respectively. Although the formation of the 3-alkyl intermediate 48 is thermodynamically favored, the acylation occurs faster in the 2-alkyl intermediates 52. Regio-selectivity is therefore dominated by the rate of formation of the acyl complexes. The modification of the phosphorus ligand and the conditions of the reaction make it possible to control the regioselectivity and prepare the 2- or 3-substituted aldehyde as the major product [78]. As far as we know, only two... 

In situ generation of azomethine imines from furan-3-carbaldehyde and ]V,N -disubstituted hydrazines followed by cycloaddition to N-methylmaleimide results in a 2.8 1 mixture of pyrazolidines 94 and 95 (X = O) separatable by chromatography. Eurther Pd(0) catalyzed cyclization involving the aldehyde and hydrazine moieties leads to the formation of benzoxepines 96 and 97 (X = O) in good yield (Scheme 17 (2003X4451)). 

In the same year, Hibino et al. reported a total synthesis of furostifoline (224) employing a new type of electrocyclic reaction (636). This cyclization proceeds through a 2-alkenyl-3-allenylindole intermediate, which is derived from 2-(fur-3-yl)-3-propargyUndole 1128. Compound 1128 was prepared starting from 2-chloroindole-3-carbaldehyde (891), furan-3-boronic acid (1124), and ethynylmagnesium bromide. 

On a commercial scale, furan is obtained from 2-formylfuran (furfural, furan-2-carbaldehyde) (see Section 6.2.7) by gas-phase decarbonylation, but in the laboratory, furans can be formed by the cyclodehydration of 1,4-dicarbonyl compounds. Heating in boiling benzene with a trace of /7-toluenesulfonic acid as a catalyst in a Dean-Stark apparatus is often effective (Scheme 6.30a). 

The reactions of substituted furo[3,2- ]pyrrole-5-carbohydrazides with 5-arylfuran-2-carbaldehydes, 4,5-disubsti-tuted furan-2-carbaldehydes, and thiophene-2-carbaldehyde have been studied <2005CEC622>. The advantage of microwave (MW) irradiation on some of these reactions was reflected in the reduced reaction time and increased yields (Table 8). The series of substituted hydrazones 241-246 was obtained from these... 

The condensation of furo[3,2- ]pyrrole-type aldehydes 8g and 265-267 with hippuric acid was carried out in dry acetic anhydride catalyzed by potassium acetate as is shown in Scheme 26. The product methyl and ethyl 2-[( )-(5-oxo-2-phenyl-l,3-oxazol-5(4//)-ylidene)methyl]furo[3,2- ]pyrrol-5-carboxylates 268a-d were obtained. The course of the reaction was compared with the reaction of 5-arylated furan-2-carbaldehydes with hippuric acid. It was found that the carbonyl group attached at G-2 of the fused system 8 is less reactive than the carbonyl group in 5-arylated furan-2-carbaldehydes in this reaction <2004MOL11>. The configuration of the carbon-carbon double bond was determined using two-dimensional (2-D) NMR spectroscopic measurements and confirmed the (E) configuration of the products. 

Thieno[3,2- ][l]benzofuran 61 was synthesized on a preparative scale starting with benzo[/ ]furan-2-carbaldehyde 344. Condensation of aldehyde 344 with 2-thioxothiazolidin-4-one in the presence of sodium acetate in acetic acid afforded 345, which by base-catalyzed hydrolysis gave 346 in good yield. Upon treatment with bromine, acid 346 was cyclized to give acid 347, which on standard decarboxylation by treatment with copper in quinoline afforded 61 in high yield (Scheme 35) <1997CCC1468>. 

Methyl 2-[3-(trifluoromethyl)phenyl]-4/7-furo[3,2-4]pyrrole-5-carboxylate 81a was made by thermolysis of the corresponding methyl 2-azido-3- 5-[3-(trifluoromethyl)phenyl]-2-furyl propenoate 378, which was formed by condensation of 5-[3-(trifluoromethyl)phenyl]furan-2-carbaldehyde 377 with methyl azidoacetate under sodium meth-oxide catalysis (Scheme 40) <2006KGS825>. 

Knoevenagel condensation of the corresponding 3-methylfuran-2-carbaldehyde 379 and 3-methybenzo[4]furan-2-carbaldehyde 382 with diethyl malonate followed by bromination with iV-bromosuccinimide (NBS) in the presence of dibenzoyl peroxide afforded bromides 380 and 383, respectively. Treatment of 380 and 383 with benzylamine, isopropylamine, /-butylamine 3-hydroxypropylamine, aniline and -toluidine in ethanol yielded furo[2,3-c]pyrroles 381 and benzo[4,5]furo[2,3-c]pyrroles 384, respectively (Scheme 41). The yields of furopyrroles 381 are only moderate (16-46%), because these compounds are highly sensitive to acid, and partially polymerized upon silica... 

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