An efficient synthesis of benzofurans and their application in the preparation of natural products of the genus Calea

The intramolecular cyclization of the β-substituted olefins methyl 2-aryloxy-3-dimethylaminopropenoates catalyzed by Lewis acids leads to a short and novel synthesis of benzofurans . When the olefins 4-dimethylamino-3-aryloxy-3-buten-2-ones were used, the cyclization process was faster and provided the corresponding substituted 2-acetylbenzofurans . Among the latter, naturally occurring compounds calebertin (), caleprunin A (), and caleprunin B () were prepared in good overall yields. These benzofurans were also obtained by direct treatment under MW irradiation of the precursors 1-aryloxypropan-2-ones with DMFDMA, followed by addition of the catalyst, resulting in a route that was one step shorter.