The gram-scale synthesis of 5,6-,
6,7-, and 7,8-chromene/chromane-type
aryne precursors and their applications in regioselective transformation
to other functional derivatives is reported. Chromene/chromane-type
arynes are generated under mild conditions, which can further undergo
[2 + 2], [3 + 2], and [4 + 2] cycloaddition reactions, nucleophilic
addition reactions, and σ-insertion reactions to produce structurally
novel substituted chromenes and chromanes. The excellent regioselectivity
of the reaction is facilitated by the oxygen-containing guiding groups
at the ortho-position of the triple bond, which can
be removed or switched to other functional groups including alkenyl,
aryl, heteroaryl, and arylamino groups.
The 2,2‐dimethyl‐2H‐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.
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