Synthesis And Structure Confirmation Of Nitrogen-containing Heterocycles Derived From Alkynyl-weinreb Amide With DBN(DBU)

1,8-Diazacyclo[5,4,0]undec-7-ene(DBU)and 1,5-dizazcyclo[4,3,0]non-5-ene(DBN)are widely utilized as non-nucleophilic strong bases in various reactions such as elimination reactions,isomerizations,condensations and cyclizations,etc.However,more and more reports have demonstrated that both DBU and DBN can act as nucleophiles.Weinreb amide compounds,which prepared from cinnamates through bromination,elimination and amidation,reacted with DBU or DBN to give different nitrogen-containing heterocycles.The structures were elucidated by nuclear magnetic resonace spectrometry(1H-NMR,13C-NMR,DEPT-135,1H-1H COSY,HSQC,HMBC,NOESY)and mass spectrometry.The influences of solvent,temperature and molar ratio of materials were investigated.The experimental results show that DBN and DBU reacted with alkynyl-Weinreb amide to provide two different types of cyclization products I and III,and competitive reaction occurred to ring opening products at the same time.Then three possible reaction mechanisms were proposed.In the above reaction,DBN played a Nnucleophile role firstly and then C-nucleophile role subsequently in forming the cyclization products I while DBU acted as a C-nucleophile firstly and then Nnucleophile role subsequently in forming cyclization product III.Meanwhile,the ring opening reaction of DBU and DBN were occured due to hydrolysis.