Strategies and Methods for the Catalytic Asymmetric Synthesis of Benzofuran/Benzopyran Fused Acetals: A Review

Abstract

Benzofuran‐ and benzopyran‐fused polycyclic acetals are found in a variety of biologically active natural products. The synthetic methods toward these class of polycyclic heterocycles have fascinated one of the most intensive pursuits in total synthesis. Nevertheless, stereoselective methods towards the rapid construction of such skeletons still remain challenging for organic chemists. Significant progress has been made in this research area in recent years, however, literature on enantioselective approaches to construct these molecules has not fully reviewed. Driven by their intriguing and complex scaffolds with potential usefulness, we compose the recent advances in this review covering all the important works in this field. We hope this review will promote future research in this area.

Synthesis of gem-Difluorinated 2,3-Dihydrobenzofurans Using Freon-22 via [4 + 1] Annulation of Difluorocarbene and Antitumor Activity Evaluation

“…Despite these advances, the direct construction of gem -difluorinated heterocyclic compounds, such as 2,3-dibenzofurans employing ClCF 2 H through a cyclization process remains a challenge and has not been successfully reported. Considering 2,3-dihydrobenzofurans are one of the key heterocyclic scaffolds that are widely present in natural products and drug candidates (Scheme a), and given our ongoing effort to develop fluorinated bioactive molecules, we herein present a practical preparation of the gem -difluorinated 2,3-dihydrobenzofurans from simple and cheap industrial material ClCF 2 H and salicylaldimines. Several adducts exhibited strong antiproliferative activity against A549, HeLa, and 4T1 cancer cell lines.…”

Asymmetric Synthesis of Hydrodibenzofurans from Norcaradienes: Kinetic Resolution via [3 + 2] Cycloaddition with Quinones

“…Hydrodibenzofuran frameworks are widely found in many bioactive natural products and pharmaceuticals (Scheme a) . The preparation of these scaffolds in a diastereo- and enantioselective manner has attracted continued interest. , [3 + 2] cycloaddition reactions of 1,4-benzoquinones are among the most powerful tools for accessing hydrobenzofuran and fused polycyclic scaffolds (Scheme b, path a) . In 2005, Zhou and Corey used chiral oxazoborolidinium triflimidate to catalyze the reaction with vinyl ether, rending a short synthesis of the pentacyclic natural product aflatoxin B2 .…”