Furyl aldehyde

Enantioselective addition of dialkylzinc to furyl aldehydes using DBNE as a chiral catalyst affords optically active furyl alcohols in up to 94% ee (eqs 15 and 16). ... 

Another early example of a continuous flow process was disclosed in 1980 by Nakamura and Morikawa [13]. It was demonstrated that recirculating an aqueous DMSO solution of fructose through a bed of strongly acidic exchange resin led to isomerization and dehydration, producing the corresponding furyl aldehyde (Scheme 5). 

Scheme 5 Proton-mediated transformation of o-fructose into a furyl aldehyde...

Aryl aldehydes Benzaldehyde Furyl aldehydes 2-Furaldehyde Ketones... 

Furyl methyl ketone was also tried with a series of olefins inhibition was operative in all systems and only traces of a copolymer with acenaphthylene were isolated at the end of a run which lasted several days. These observations are compatible with the higher basicity of this ketone compared with that of the corresponding aldehyde. 

The intramolecular cyclization of diketo-enals and keto-enals was accomplished by the combination of a cationic Rh complex and fn(2-furyl)phos-phine (2 - Fur3P). The corresponding bicyclic hydroxy-aldehydes were produced in good to excellent yields, as demonstrated by the formation of 74,76 and 78 (Scheme 22) [36]. 

The Mannich reaction of secondary amines R NH (dibenzylamine, piperidine, morpholine, etc.), aldehydes R2CHO (R2 = alkyl, Ph or 2-furyl) and thiols R3SH (R3 = alkyl, Ph or benzyl) results in a-amino sulphides, which react with Grignard compounds to give tertiary amines in good yields (equation 47)136. 

The reaction with aromatic aldehydes (R=Ph, p-Tol, P-CIC6H4, 2-furyl) is not strongly stereoselective, the E geometry being preferred. In the presence of HMPA (30%) the Z isomers become predominant. In the case of aliphatic aldehydes (R=/-C3H7, C3H7) the Z geometry is preferred in both solvent systems. 

The imidates (62) also serve as nitrile yhde synthons via cycloaddition and subsequent spontaneous elimination of ethanol (34,35). Cycloadditions were carried out to aldehydes, leading to 2-oxazolines (e.g., 64) and to isocyanates and isothiocyanates. In the preparation of the 2-oxazolines, a solvent-less mixture of the imidate and the required aldehyde were heated at 70 °C and the cycloadducts 64 (R=Ph, 2-furyl, Mc2CH, 2-HO C6H4, 2-pyridyl, cinnamyl) were isolated in yields of 64—91%. 

Synthesis of the enantiomerically pure (5)-chroman-2-carbaldehyde (257) follows a similar route to the above, but the chirality is introduced through the ketone (256) (82CC205). A particularly interesting feature of this synthesis is the derivation of the diol (255) from 2-methyl-3-(2-furyl)propenal using fermenting baker s yeast. Furthermore, the fermentation also produces the chiral alcohol (258), a source of the C15 unit which is the second component along with the aldehyde (257) in an a-tocopherol synthesis. 

Reaction with Further Electrophiles of Group IVA (Sl,Ge,Sn). IV-Silylated aziridines can be prepared from ethyleneimine by amination of chlorosilanes in the presence of an HC1 acceptor, by dehydrocondensation with an organosilicon hydride or by cleavage of a silicon—carbon bond in 2-furyl-, 2-thienyl-, benzyl-, or allylsilanes in the presence of an alkali metal catalyst (262—266). N-Silylated aziridines can react with carboxylic anhydrides to give acylated aziridines, eg, A/-acetylaziridine [460-07-1] in high yields (267). At high temperatures, A/-silylaziridines can be dimerized to piperazines (268). Aldehydes can be inserted... 

The cycloaddition of diazomethane to SchifT bases from heterocyclic aldehydes and anilines provides a useful route to heterocyclic substituted triazolines. Unlike olefins bearing heterocyclic substituents, the heterocyclic imines can be obtained readily by reaction of the appropriate aldehyde and amine thus the diazomethane-imine addition has greater scope than the olefin-azide reaction. NMR spectroscopic studies of the orientation of addition are in accord with previously reported mechanistic considerations (see, e.g., Scheme 93).329 In addition to the influence of the N-aryl group, the electron-withdrawing power of the heterocyclic substituent on the Schiff-base carbon also has a substantial effect on imine reactivity, in the order 2-quinolyl 2-, 3-, or 4-pyridyl > phenyl > 2-thienyl as 2-furyl.329... 

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