Synthesis of novel tetrahydro-1H-pyrazolo[4,3-c]pyridines via intramolecular nitrilimine cycloaddition

The preparation of novel tetrahydro-1H-pyrazolo[4,3-c]pyridines is reported. Pivotal to the synthesis of these compounds was the development of mild reaction conditions to generate a highly functionalized nitrilimine capable of undergoing an intramolecular cycloaddition with a tethered alkyne. The desired cycloadduct was formed as an equal mixture of diastereomers.