Formal [3 + 3] Cycloaddition Approach to Chromenes and Chromanes. Concise Total Syntheses of (±)-Rhododaurichromanic Acids A and B and Methyl (±)-Daurichromenic Ester

Abstract

[reaction: see text] Total syntheses of (+/-)-rhododaurichromanic acids A and B and methyl (+/-)-daurichromenic ester are described here. Despite the complex appearances of these compounds, their syntheses are completed in six steps with a 15% overall yield as a mixture by featuring our formal oxa-[3 + 3] cycloaddition methodology.