Design of a Functional Chromene‐Type Kobayashi Precursor: Gram‐Scale Total Synthesis of Natural Xanthones by Highly Regioselective Aryne Annulation

The 2,2‐dimethyl‐2 H ‐chromene motif is widely found in many bioactive molecules, and is a privileged structure in the pharmaceutical arena. We have developed a concise and regioselective approach to chromenes and chromanes through an aryne‐based synthetic strategy. A practical, gram‐scale synthetic route to a chromene‐type aryne precursor was explored. Subsequently, cyclization under mild conditions afforded tetracyclic xanthone skeletons with excellent regioselectivity. Our approach provides a concise strategy for the gram‐scale synthesis of chromene‐type xanthones such as 6‐deoxyisojacareubin, cylindroxanthone D, staudtiixanthone D, brasilixanthone A and cudracuspixanthone O.