The Formation of Seven-Membered Heterocycles under Mild Pictet–Spengler Conditions: A Route to Pyrazolo[3,4]benzodiazepines

Reported is a method for the synthesis of seven-membered heterocycles via a Pictet-Spengler condensation reaction under very mild conditions. High substrate scope allows for use of aldehydes using catalytic amounts of acetic acid yielding 39-90% and ketones using catalytic amounts of trifluoroacetic acid yielding 25-83%.