Construction of the 5,10b‐Phenanthridine Skeleton Using [3+2]‐Cycloaddition of a Non‐Stabilized Azomethine Ylide: Total Synthesis of (±)‐Maritidine and (±)‐Crinine Alkaloids

Abstract

Abstract Vicinal quaternary and tertiary stereocenters of the 5,10b‐phenanthridine skeleton 1 are constructed simultaneously in one step by the [3+2]‐cycloaddition of non‐stabilized azomethine ylide 9 , generated by sequential double desilylation of 10 utilizing silver(I) fluoride as a one‐electron oxidant. The regio‐ as well as stereochemical origin of this cycloaddition reaction is explained through a favorable transition state 9″ . The strategy is successfully applied for the total synthesis of the biologically active alkaloids (±)‐maritidine ( 1a ), (±)‐crinine ( 1b ), and their analogues ( 1d , 1e , and 1f ).