Hydrogenation of furan derivatives

Hydrogenation of Substituted Furan Derivatives Although one of the earliest approaches to the synthesis of nonactic acid involved catalytic hydrogenation of an appropriately 2,5-disubstituted furan, the hydrogenation of furan derivatives is limited by the formidable problem of controlling the well separated acyclic stereocentres at C-2 and C-8. 

Fio. 49. The volcano-shaped curves in tho hydrogenation of furan derivatives. The numbering of the reactions corresponds to that of Table XVIII. 

Nakagawa Y, Tomishige K (2010) Total hydrogenation of furan derivatives over silica-supported Ni-Pd alloy catalyst. Catal Commun 12 154-156... 

Similar procedures to those used for the catalytic hydrogenation of furan and thiophene can usually be applied to the functional derivatives of these heterocycles. 

Pyrylium salts are also suitable for the preparation of furans.7Z,7S Oxidation of these salts by aqueous hydrogen peroxide in the presence of perchloric acid leads to ring contraction, with the formation of furan derivatives. Nenitzescu and Balaban described the following example72 ... 

The catalytic hydrogenation of furan and its derivatives is strongly dependent on reaction conditions and catalysts employed. A review is available.188 It is possible to classify the results of these reactions into three main groups ... 

Derivation (1) Catalytic hydrogenation of furan with nickel catalyst. (2) Acid-catalyzed dehydration of 1,4-butanediol. 

Thiophenes are formed by different reactions. The general reaction is that of furan derivatives with hydrogen sulfide (Figure 8.72). This mechanism is assumed, for example, in the formation of some thiophene derivatives from 4-hydroxy-2//-furan-3-ones. Alkylth-iophenes substituted in positions C-2 and C-3 may arise in reactions of 2-mercaptoethanal with unsaturated aldehydes, such as acrolein or but-2-enal (Figure 8.73). 2-Mercaptoethanal is a product of Strecker degradation of cysteine. 

Furan resin based binders are prepared by the acid-catalyzed (co)polymerization of furfuryl alcohol, which is obtained by hydrogenation of - furfural, derived of fibrous 1 -products of agricultural production, such as - bagasse, - com, com cobs, oats, wood ( luran derivatives). 

It is produced, aside from several other technical possibilities, by - hydrogenation of - furan, which is derived from RR. 

The oxidative reaction of furan with bromine in methanol solution or an electrochemical process using sodium bromide produces 2,5-dimethoxy-2,5-dihydrofuran (19), which is a cycHc acetal of maleic dialdehyde. The double bond in (19) can be easily hydrogenated to produce the corresponding succindialdehyde derivative. Both products find appHcation in photography and as embalming materials, as well as other uses. 

The addition of p-quinone to enamines normally produces furan derivatives, especially when the enamine possesses a 3 hydrogen (see Section III. A). 1,2 Cycloaddition is claimed to take place to give a cyclobutane derivative when p-quinone and an enamine with no jS hydrogens are allowed to react at low temperatures (51). However, little evidence is reported to verify this structural assignment, and the actual structure probably is a benzofuranol (52). Reaction of a dienamine (formed in situ) with p-quinone in the presence... 

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