Ene reactions of 2-borylated α-methylstyrenes a practical route to 4-methylenechromanes and derivatives
Abstract
4-Methylenechromanes were prepared via a three-step process from 2-borylated -methylstyrenes. This sequence is based on a key glyoxylate-ene reaction catalyzed by scandium(III) triflate. The resulting -hydroxy boronates, which cyclise to seven-membered homologues of benzoxaborole on silica gel, were cleanly oxidized with sodium perborate, then cyclised under Mitsunobu conditions. Additionally, several further functional transformations of 4-methylenechromanes or their precursors were carried out to illustrate the synthetic potential of these intermediates.
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Chemical Sciences
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