Total Synthesis of the Furopyran Lignans Sumatranin A–D and the Proposed Structure of Sumatranin H

Sumatranins A–D are lignans isolated from the twigs of Cleistanthus sumatranus that contain a previously unseen furopyran in a tetrahydro-furo[2,3-b]chromene tricyclic system. In this work, sumatranins A–D were enantioselectively synthesized utilizing an Evans aldol reaction followed by acid-catalyzed cyclization as key steps. Additionally, the proposed structure of dibenzylbutyrolactone lignan sumatranin H, an apparent biosynthetic precursor to the furopyran lignans, was synthesized but determined to be inconsistent with the previously isolated data. The synthetic routes developed allows for the construction of a wide range of sumatranin-type lignans or unnatural analogues.