NUCLEOPHILIC REACTION OF 1,8-DIAZABICYCLO[5.4.0]UNDEC-7-ENE AND 1,5-DIAZABICYCLO[4.3.0]NON-5-ENE WITH METHYL PHEOPHORBIDE-A - UNEXPECTED PRODUCTS

Trialkylsilyl triflates promote the direct nucleophilic reaction of '' non-nucleophilic DBU and DBN'' with methyl pheophorbide a (1) to give substituted chlorin e(6) amides 3 and 4, where the bicyclic bases have undergone ring opening. The reaction most likely results from coordin ation of trialkylsilyl triflates to the beta-ketoester in 1, forming a n ion-pair intermediate 6. The adduct 6 is so strongly electron-defici ent that it can electrophilically attack the nonbonding nitrogen elect ron pairs in DBU and DBN.