Furans and benzofurans

Furanes and benzofuranes in which an oxygenated ring is condensed into one or more aromatic rings. 

Fragmentation Losses from the molecular ions are 1, 29, and 30 Daltons with the loss of 29 (CHO) being characteristic of cyclic ethers. This loss also appears in the mass spectra of unsaturated cyclic ethers, such as furans and benzofurans. The fragmentation of saturated cyclic ethers generally shows a M — 1 ion. 

As was the case for pyrroles, fluorine substituents at the 2-position are greatly deshielded relative to those at the 3-position of furans and benzofurans (Scheme 3.65). 

Five-membered ring systems furans and benzofurans... 

Five-Membered Ring Systems Furans and Benzofurans... 

Furans and benzofurans continue to play an important role in the field of heterocyclic chemistry because their skeletons are present in many naturally occurring molecules, and they serve also as extremely useful precursors or intermediates towards the realization of many complex molecules. The authors of the present chapter have placed their attention on the more interesting applications and syntheses of these families of compounds, instead of executing an exhaustive literature search of all the relevant papers that were recorded in 2000. 

Ohta s group coupled aryl bromides such as 2-bromonitrobenzene with benzofuran [85]. The heteroaryl Heck reaction took place at the more electron-rich C(2) position of benzofuran. They later described the heteroaryl Heck reactions of chloropyrazines with both furan and benzofuran [86],... 

Pd-catalyzed alkoxylcarbonylation of furan and benzofuran was achieved in the presence of Hg(02CCF3)2 in ethanol with low efficiency [107]. Other heterocycles including thiophene and pyrrole were also carbonylated to give the corresponding esters in low yields using the same method. 

The most unique feature of furan synthesis using palladium chemistry is heteroannulation. Enones, ynones and ynols all have been annulated into furans and benzofurans. More importantly, trapping the reactive Pd(II) intermediates at different stages with electrophiles offers unique opportunities to synthesize substituted furans and benzofurans. 

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