Modular Approach to Benzofurans, 2H-Chromenes and Benzoxepines via Claisen Rearrangement and Ring-Closing Metathesis: Access to Phenylpropanoids.

Benzofurans, 2H-chromenes and benzoxepines are key structural elements present in several natural products and pharmaceuticals. Here, we describe an easy-to-execute strategy for the synthesis of benzofurans, 2H-chromenes and benzoxepines, by employing Claisen rearrangement and ring-closing metathesis as key steps. A variety of phenols were converted into useful oxacycles in good to excellent yields. The ring-closing metathesis approach has been used to produce phenylpropanoid natural products. Examples described here include, the naturally occurring benzofurans such as 7-methoxywutaifuranal, 7-methoxywutaifuranol, 7-methoxywutaifuranate and the O-prenylated natural products like boropinic acid, boropinols A and C.