Palladium[0]-mediated aminospirocyclization of tertiary allylic sulfones. Stereospecific construction of the azabicyclic ring system of cephalotaxine

Abstract

Tertiary allylic sulfones which bear a secondary aminopropyl moiety undergo smooth palladium[0]-mediated spirocyclization. The reaction proceeds via a π-allyl intermediate and the resultant azabicyclic product is formed with net retention of sulfone stereochemistry. The use of tetramethylguanidine as companion base is required for high yielding reactions.