Oxidative generation of isobenzofurans from phthalans: application to the formal synthesis of (±)-morphine
Mirai Kage1, Hiroyuki Yamakoshi1, Manami Tabata1
1Graduate School of Pharmaceutical Sciences, Nagoya City University 3-1 Tanabe-dori, Mizuho-ku Nagoya 467-8603 Japan nakamura@phar.nagoya-cu.ac.jp.
Abstract:
Treatment of phthalan derivatives with p-chloranil in dodecane in the presence of molecular sieves at 160-200 °C allowed the generation of unstabilized isobenzofurans, which underwent intramolecular Diels-Alder reaction to give endo cycloadducts exclusively. The cycloaddition turned out to be reversible, providing an equilibrium mixture of endo adducts when heating a substrate with a stereocenter on the tether. We also demonstrated the regioselective allylation of an oxygen-bridged cycloadduct upon exposure to EtAlCl2 in the presence of allyltrimethylsilane, and the conversion to Rice's intermediate completed a formal synthesis of (±)-morphine.
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