Current status of synthesis of deprotected tridents by substituent variations of aza-ACE reaction

The N-bridged [n]polynorbornanes are a new class of N-bridged norbornanes that have become available using cycloaddition protocols developed by our group. [1] The basis for the synthesis is a dipolar cycloaddition reaction involving benzonorbornadienes as the dipolarophile and the 1,3-dipole formed by the ring-opening of a 5-azabicyclo[2.1.0]pentane. This reaction (the aza-ACE reaction [2]) requires that the aziridine be N-substituted thereby leading to the corresponding N-substituted polynorbornane (the trident). There are limitations on the type of substituent that can be introduced into the trident (eg the CBZ groups fail) and it has been necessary to find alternative groups that can be removed from the trident if the NH-bridged systems are to be accessed. This paper presents the results of our recent endeavours toward this goal of preparing NH-bridged tridents, especially those containing more than one NH-bridge.