General Method for Synthesis of Erythrinan and Homoerythrinan Alkaloids (2): Application of Pummerer-Type Reaction to the Synthesis of Homoerythrinan Ring System

The synthesis of cyclohomoerythrinan (2a), a potential intermediate to homoerythrian alkaloids, was achieved by a Pummerer-Type cyclization of the hydroindole sulfoxide ( l l ) , which was prepared from the dioxopyrroline (6) in five steps via a [2+2] photocycloaddition reaction foUowed by an anionic 1,3-shift.Recently, we developed a new method for constructing erythrinan ring system by a Pummerer-type cyclization.'A typical example is the synthesis of the cycloerythrian (I),' which is one of the key intermediates to