ortho-Quinone Methides from para-Quinones: Total Synthesis of Rubioncolin B

摘要

ortho-Quinone methides have proven to be remarkably versatile reactive intermediates, and many methodologies, generally relying on benzylic activation of ortho-substituted phenols, have been developed to access them. In Nature, ortho-quinone methides appear to be often formed via tautomerization of alkyl-substituted para-quinones (eqs 1 and 2). This surprisingly facile tautomerization can be a powerful tool in total synthesis as well. Recently, we reported the tautomeriza-tion/electrocyclization of prenylated para-quinones as a strategy for the synthesis of chromene natural products (eq 1). Herein, we show that this method can be modified to include intramolecular Diels-Alder (IMDA) cycloadditions (eq 2). These efforts have resulted in a concise total synthesis of the complex naphthohydroquinone dimer rubioncolin B(1).