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 ringclosing 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, 7methoxywutaifuranate and the O-prenylated natural products like boropinic acid, boropinols A and C.

No abstract

Benzofurans and benzoxepines are key structural elements present in several natural products and medicinally important targets. Here, we describe an easy‐to‐execute strategy for the synthesis of benzofurans and benzoxepines, by employing Claisen rearrangement and ring‐closing metathesis (RCM) as key steps. Amino acid L‐tyrosine and 1,8‐dihydroxy‐anthraquinone were converted into modified oxacycles in good yields. The RCM approach has been used to produce bis‐fused benzofuran, bis‐fused benzoxepine, and unusual α‐amino acid (AAA) derivatives containing heterocyclic units. Unusual AAA derivatives are among the most important source for new peptide drugs and these AAA derivatives containing oxacycles are useful in designing many natural and unnatural products. Bis‐fused benzofuran and bis‐fused benzoxepine derivatives were also synthesized by the application of double Claisen rearrangement and two‐directional RCM as key steps starting with 1,8‐dihydroxy anthraquinone.

We disclose an approach to a library of novel multidimensional O‐heterocycles based on a rigid, tetrahedral core. New derivatives of tetraphenylmethane (TPM) have been synthesized by employing Claisen rearrangement (CR) and ring‐closing metathesis (RCM) as key steps. Mono‐, di‐, tri‐, and tetra‐substituted benzofurans, 2H‐chromenes, and benzoxepine derivatives are reported. Various heterocyclic cores present in these compounds are key structural elements present in several natural products and pharmaceuticals as well as valuable precursors for the construction of complex molecules with the tetrahedral framework. To the best of our knowledge, this is the first report involving the synthesis of five‐, six‐, and seven‐membered O‐heterocycles in TPM core and the basecatalyzed inexpensive synthesis of several isomerized intermediates that are useful to prepare oxacycles such as benzofuran and 2H‐chromenes. The symmetrical and unsymmetrical one, two, three, and four‐armed architecture of TPM makes it a valuable starting point for building complex molecular and supramolecular architectures. To expand the unmet chemical space of the TPM core, we have prepared twenty new derivatives by a unified approach. Additionally, we report a simple, catalyst‐free, and inexpensive recipe for double bond isomerization based on KOtBu to assemble various oxacycles derived from different trityl chloride derivatives.

No abstract