Furan-Terminated N-Acyliminium Ion Initiated Cyclizations in Alkaloid Synthesis.

A study of the utility of furan-terminated N-acyliminium ion initiated cyclizations for the synthesis of linearly fused alkaloid precursors (Figure 2) is presented. The outcome of the cyclization event depends on the position of furan tether attachment (2 vs 3), tether length, and furan 5-substituent (R = H, CH(3), Ar). 3-Substituted furans cyclized to form 6- and 7-membered ring containing furans 35-38, 50, and 51 in good to excellent yields.