SCHEDULED MAINTENANCE
Cyclopropanation of the chalcone (3) with dimethylsulphonium ethoxycarbonylmethylide affords a 1 : 1 mixture of the cyclopropanyl keto-ester epimers (4) and (5); both stannic chloride and boron trifluoride etherate in nitromethane catalyse the stereoselective cyclisation of this mixture to the tetralone (2), the known podophyllotoxin precursor, in 51% overall yield.
W. S. Murphy and S. Wattanasin, J. Chem. Soc., Chem. Commun., 1980, 262 DOI: 10.1039/C39800000262
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