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 coordination of trialkylsilyl triflates to the beta-ketoester in 1, forming an ion-pair intermediate 6. The adduct 6 is so strongly electron-deficient that it can electrophilically attack the nonbonding nitrogen electron pairs in DBU and DBN.