Furans alkene coupling reactions

Heteroaromatic compounds show similar behavior to benzene derivatives. Furan, pyrrole, thiophene, benzofuran, indole, benzothiophene, and their related compounds undergo CDC reactions with alkenes. In the case of furan, the coupling reactions with acrylates, acrylonitrile, styrenes, and... 

Oxidative cross-coupling with alkenes is possible with Pd(OAc)2 [109], The reaction proceeds by the palladation of benzene to form phenylpalladium acetate (164), followed by alkene insertion and elimination of /1-hydrogen. Heteroaromatics such as furan and thiophene react more easily than benzene [109]. Stilbene (177) is formed by the reaction of benzene and styrene. The complex skeleton of paraberquamide 179 was obtained in 80% yield by the Pd(II)-promoted coupling of the indole ring with the double bond in 178, followed by reduction of the intermediate with NaBELt [110]. 

Halofuran and halothiophene derivatives undergo photochemical reactions with arylalkenes and arylalkynes and with benzo[6]furan513,514. With the arylalkenes and aryl-alkynes, heteroarylation takes place at the terminal alkene or alkyne carbon atom, while benzo[6]furan is substituted at position 2. The experimental results are interpreted in terms of solvent-separated or contact radical ion pairs. Iodothiophene and iodofuran derivatives can also be used to synthesize derivatives of benzimidazole by means of photochemical coupling515. The reaction of 5-iodothiophene-2-carboxaldehyde (157) with benzimidazole (158) giving the coupling product 159 is illustrated in equation 131. 

Topics reviewed during the year include the photochemistry of indoles, sulfoxides, pyrazoles and isothiazoles, (S-hetero)cyclic unsaturated carbonyl compounds, photoinduced single electron transfer (SET) reactions of amines and of azo compounds, SET reactions of organosilanes and organostannanes with Qo and ketones, photochromic polypeptides and di(hetero)arylethenes, processes in chromophore sequences on a-helical polypeptides,aryl-aryl coupling in furans, thiophenes and pyrroles," [3+2]cycloaddition of aromatic nitriles (and esters) with alkenes, and reactions of benzylsilane derivatives. ... 

The arene substrates are not limited to simple benzene derivatives. A variety of het-eroarenes can also participate in alkene arylations to generate the desired coupling products. Stoichiometric oxidative coupling of aromatic heterocycles such as furan, thiophene, selenophene, A-methylpyrrole, benzofiiran and benzothiophene with a variety of alkenes, including acrylonitrile, styrene and methyl acrylate, have been extensively studied by Fu-jiwara and coworkers [8]. Furan, thiophene, selenophene and A-methylpyrrole are easily alkenylated with alkenes to give 2-alkenylated and 2,5-dialkenylated heterocycles in relatively low yields (3 6%) [8a], while the reactions of benzofuran and benzothiophene with alkenes produced a mixture of 2- and 3-alkenylated products [8b]. 

The palladium(II)-catalysed alkenylation of heterocycles has also been studied extensively. Fujiwara and coworkers [8b, 26] reported that the reactions of furan and thiophene with alkenes such as methyl acrylate and acrylonitrile in the presence of 2 mol% Pd(OAc)2 and 2 equiv of Cu(OAc)2 under atmospheric oxygen or air produced both 2-alkenylated and 2,5-dialkenylated products. This method, however, was not particularly synthetically useful due to the low yields of the reactions (0.3-39%). Tsuji and Nagashima [21] also observed that furans 31a-c reacted with acrylates 4b and 4c to produce monoalkenylated compounds 32a-c, where the furan has been functionalized solely at the 2-position (or the 5-position if the 2-position is substituted) in moderate to good yields. Even a furan with an electron-withdrawing substituent (2-furaldehyde, 31c) participated in the oxidative coupling to yield a moderate 34% yield of the arylation... 

The CDC reaction of arenes and alkenes can be applied to heteroaromatic compounds. Coupling with furan, thiophene, pyrrole, benzofuran. 

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