[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.
Formal [3 + 3] Cycloaddition Approach to Chromenes and Chromanes. Concise Total Syntheses of (±)-Rhododaurichromanic Acids A and B and Methyl (±)-Daurichromenic Ester. -Rhododaurichromanic acids A and B [compound (IIa) and (IIb), respectively] are prepared as epimeric mixture in six steps in a 15% overall yield by a route involving the photochemical [2 + 2] cycloaddition of daurichromenic ester (I).-(KURDYUMOV, A. V.; HSUNG*, R. P.; IHLEN, K.; WANG, J.; Org. Lett. 5 (2003) 21, 3935-3938; Dep. Chem., Univ. Minn., Minneapolis, MN 55455, USA; Eng.) -Klein 09-241
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