An Unprecedented Cyclization

Successful Approach to Strychnine Part 2 - An Unprecedented [2 + 2 + 2]Cyclization 

Successful Approach to Strychnine Part 3 - Formation of the E Ring by Oxidative Demetallation/Intramolecular Conjugate Addition 

In preparation for E ring closure, the appended nitrogen center required deacylation for sufficient nucleophilicity. Of concern were the 

Surprisingly, 43 was consistently isolated as the C12-05 diene, as opposed to a system in conjugation with the amide carbonyl. That this was in fact the kinetic product was revealed by isomerization of 43 to 44 upon exposure to sodium methoxide. However, 44 was unstable and difficult to purify, not surprising, considering its functionality. If this problem could be resolved later, secondary amine 43 would represent a 

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An unprecedented cyclization (Scheme 15), by C-16—C-2 bonding, is ob-served when deoxyvobasine (52) is treated with phosphoric acid giving (53a), or with lithium aluminium hydride giving (53b). 

Finally, an alternative intramolecular Csp -N bond coupling was described by Mai [13]. In this case, the authors developed conditions for the oxidative addition of an aniline to an imine group within the same molecule 20 to arrive at 2-arylated benzimidazoles 21. The reaction is of ample scope. The mechanistic details are unclear at present and the authors propose an initial interaction between the tosyl-amido group and the hypervalent iodine reagent to initiate electrophilic amination chemistry, which is followed by an unprecedented cyclization upon the aldimine group. 

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