Stereoselective furan-iminium cation cyclization in the construction of the core structure of manzamine A.

[reaction: see text] A new type of furan-iminium cation cyclization was developed and used to construct the ABC ring of manzamine A. The cyclization proceeded at the 2-position with complete regio- and stereoselectivity to give a spiro-center. The product was efficiently converted to the highly substituted core structure of manzamine A.