General Synthesis of 3‐Azabicyclo[3.1.1]heptanes and Evaluation of Their Properties as Saturated Isosteres**

A general approach to 3-azabicyclo[3.1.1]heptanes by reduction of spirocyclic oxetanyl nitriles was developed. The mechanism, scope, and scalability of this transformation were studied. The core was incorporated into the structure of the antihistamine drug Rupatidine instead of the pyridine ring, which led to a dramatic improvement in physicochemical properties.