Site-Selective Reaction of Enaminones and Enamine Esters for the Synthesis of Novel Diverse Morphan Derivatives

An
efficient and concise protocol was developed for the synthesis
of diverse morphan derivatives 5–7 by the Michael and aza-Michael reaction of different types of quinone
monoketals 1 or quinone imine ketals 2 with
enaminones or enamine esters 3 promoted by 1,8-diazabicyclo[5.4.0]­undec-7-ene
in acetone at reflux. Notably, when cyclic enaminone 4 was used as a substrate in the aza-Michael and 1,2-addition reactions
with quinone monoketals 1, they gave another novel morphan 8. This method is suitable for parallel synthesis of bridged
ring compounds. As a result, highly diverse morphan derivatives were
easily and efficiently prepared by the Michael/aza-Michael or aza-Michael/1,2-addition
reactions.