Benzofuran-containing compounds, synthesis

Transition metal-catalyzed cross-coupling and C-H activation have become an important method for the formation of carbon-carbon bonds in the synthesis of furan and benzofuran containing pharmaceutical compounds. The reaction conditions required for these transformations are generally mild and tolerant of a number of different functional groups including ethers, esters, and amines to name a few. 

The synthesis of photochromic compounds containing combinations of benzothiophene and thiophene 70 (04JPP(A)97, 09JMS100), indene 71 (06TL1267), or benzofuran rings 72 and 73 (06BCJ1100, 08BCSJ644) was documented (Scheme 22). 

While the synthesis of benzofuran derivatives from suitable furan derivatives has been comparatively little investigated, the synthesis of fused two-ring and three-ring compounds containing a pyridine nucleus from furan derivatives has been more successful furo[3,2-c]pyridines (345),752>753 2,3-dihydrofuro[2,3-a ]quinolines (from 4,5-dihydro-3-furoic acid),754 acrophyllin (346), and 7-hydroxydictamnine (347) (from ethyl 2-ethoxy-4-oxo-4,5-dihydrofuran-3-carboxylate),755 are examples of compounds in this class which have been prepared. 

A similar principle for the formation of molecules was used for the synthesis of the photochromic compounds containing combinations of benzothiophene (benzofuran) and indene 98 [104], pyrazole [105], or benzofuran cycles 99 and 100 [106,107]. 

Benzofuran derivatives are one of the most important oxygen-containing heterocycles. Many natural or synthetic compounds containing benzofuran skeletons have been foxmd to possess remarkable activity as agrochemicals and pharmaceuticals [66]. Many methods have been developed for the synthesis of benzofuran in homogeneous and heterogeneous catalytic pathway. However, only the heterogeneously catalyzed reactions will be discussed here. 

---