The stereospecific synthesis of (-)-(8r) and (-)-(8s)-methylcanadine
Baird PD., Blagga J., Davies SG., H. Sutton K.
Regioselective complexation of the dimethoxy arene ring of canadine to the Cr(CO)2 moiety gives two diastereoisomers which are separated by flash chromatography. Deprotonatlon of either diastereoisomer with n-butyllithium followed by addition of methyl iodide or trimethylsilyl chloride gives C11-methyl- or -trimethylsilylcanadine after decomplexatlon. Each diastereoisomer of the C11-trimethylsilylcanadine complex may be treated with base and methyl iodide to give, after desilylation and decomplexatlon, the enantiomerically pure (-)-(8R) and (-)-(8S) methyl canadines; racemic samples of C8-methylcanadines are prepared via an independent route. © 1988.