Furan photochemical reaction with alkenes

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. 

Cantrell, T. S., Photochemical reactions of 2-acylthiophenes, -furans and -pyrroles with alkenes, J. Org. Chem., 39, 2242,1974. 

The cyclic /J-dicarbonyl iodonium ylides can undergo [3 + 2] cycloaddition reactions with various substrates under catalytic or photochemical conditions, presumably via a stepwise mechanism [153-156]. In a recent example, iodonium ylide 211, derived from dimedone, undergoes dirhodium(II) catalyzed thermal [3+ 2]-cycloaddition with acetylenes 212 to form the corresponding furans 213 (Scheme 75). Under photochemical conditions ylide 211 reacts with various alkenes 214 to form dihydrofuran derivatives 215 [156]. 

Heteroatom Wittig chemistry also includes reactions of N-sulfonyl imines. It was demostrated that these compounds underwent olefination reactions with nonstabilized phosphonium ylides under mild conditions to afford an array of both Z- and E-isomers of 1,2-disubstituted alkenes, allylic alcohols, and allylic amines.Additionally, studies of the reactions of 5-bromo-4,6-dimethyl-2-thioxo-l,2-dihydropyridine-3-carboni-trile and thiazolidinone with phosphorus ylides have proved the formation of new phosphonium ylides. Annulations via P-ylides are a common occurrence in the literature. For example, on photochemical irradiation, phosphonium-iodonium ylides were shown to undergo 1,3-dipolar cycloaddition reactions with triple bonds, via a carbene intermediate, to yield furans. " Even more common are the reactions of Morita-Baylis-Hillman (MBH) acetates and carbonates. Zhou et al. demostrated that these substrates were able to generate very reactive 1,3-dipoles in the presence of tertiary phosphines the dipoles then underwent cycloaddition reactions to yield annulation products (Scheme 16). ... 

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