Transannular cyclizations imines

Diastereoselective reaction of diimines with sodium in ether leads to the formation of macrocyclic ethers of the type (32 equation 67) and (33 equation 68) in modest yields, However, there are no reports of examples using the templating effect of low-valent transition metals, as used to good effect for intramolecular carbonyl couplings. Electrochemical reduction of imines has been used to produce a variety of bicyclic structures via cyclization-aromatization (equation 69) or transannular cyclization (equation 70). ... 

Several other biomimetic approaches to the synthesis of cephalotaxine have also been reported. In 1977, Kupchan etal. (72,73) prepared tetrahy-droisoquinoline 214, which underwent intramolecular oxidative coupling to 215 by means of vanadium(V) oxytrifluoride and trifluoroacetic acid/ trifluoroacetic anhydride (Scheme 38). Treatment of 215 with 1 N sodium hydroxide in methanol yielded the ring-expanded product, imine 216, which was converted in five steps to amine 217. Transannular cyclization of 217... 

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