Acid-catalyzed cyclization of benzalaminoacetal results in the formation of the isoquinoline nucleus. This reaction, first reported by Pomeranz and Fritsch, has been used in the synthesis of a variety of isoquinoline compounds. The process is carried out in two stages. In step one, a condensation leads to the benzalaminacetal. In step two, a ring closure leads to the isoquinoline. An alternative route involves the condensation of the corresponding benzylamine with glyoxal semiacetal. The yield of isoquinoline products varies widely. The Pomeranz-Fritsch synthesis offers the possibility of preparing isoquinolines with the substituent groups in an orientation difficult to achieve with other methods.