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. Author manuscript; available in PMC: 2009 Mar 18.
Published in final edited form as: Nature. 2008 Sep 18;455(7211):323–332. doi: 10.1038/nature07370

Figure 6. Enantioselective Pictet–Spengler cyclization toward harmicine (35).

Figure 6

Facile prepartion of hydroxylactam 31 facilitated the asymmetric Pictet–Spengler cyclization catalyzed by thiourea 32. The enantioselective N-acyl iminium ion cyclization enabled rapid construction of the alkaloid (+)-harmicine following this key transformation.81 TMSCl, chlorotrimethylsilane; THF, tetrahydrofuran. (Reduced to 45%)