Concise synthesis of tylophorine

The phenanthroindolizidine alkaloid tylophorine has been synthesized in the (R)- and racemic forms. One of the routes involves three steps from a known compound employing a Stevens rearrangement as the pivotal reaction. The phenanthrene moiety was constructed by either a base-catalyzed cyclization of 2-alkynylbiphenyls or a double Suzuki coupling of a 2,2′-dibromobiphenyl with vic-bis(pinacolatoboryl)alkene in other routes.

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