The alkene (2) obtained directly from the reaction of dimethyl maleate with the pyrone (1) is converted into (±)-podophyllotoxin (12) in seven steps and 24% overall yield; novel steps include the epimerisation of (9) at C-3 using 1,8-diazabicyclo[5.4.0]undec′7-ene (DBU) and selective oxidation of (8) to (9) using (Bun3Sn)2O–I2.
D. W. Jones and A. M. Thompson, J. Chem. Soc., Chem. Commun., 1989, 1370 DOI: 10.1039/C39890001370
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