Pomeranz-Fritsch isoquinoline ring closure

Modified Pomeranz-Fritsch isoquinoline ring closure... 

Polysulfides s. Trisulfides Pomeranz-Fritsch isoquinoline ring closure 27, 940 Position shift (s. a. Interchange, positional, Migration, Rearrangement)... 

Trifluoroacetic anhydride I boron fluoride Ring closure with acetals Pomeranz-Fritsch isoquinoline ring closure... 

This reaction was first and concurrently reported by Pomeranz and Fritsch in 1893. It is the synthesis of isoquinolines via an acid-promoted electrophilic cyclization of benza-laminoacetals prepared from aromatic aldehydes and aminoacetals. Therefore, this reaction is known as the Pomeranz-Fritsch cycUzation, Pomeranz-Fritsch isoquinoline synthesis, Pomeranz-Fritsch reaction," Pomeranz-Fritsch ring closure, Pomeranz-Fritsch ring synthesis, or Pomeranz-Fritsch synthesis. ... 

The Pomeranz-Fritsch synthesis [Eqs. (1) and (2)]1 is the only isoquinoline synthesis involving a simple two-step sequence from common starting materials. Furthermore, it is one of the few methods which can be used to prepare isoquinolines substituted in the 7- and 8-positions. The first step, Schiff base formation [Eq. (1)], takes place readily, but the ring closure [Eq. (2)] is difficult. The yields vary markedly with the concentration of H2S04 and are generally low. Frequently the reaction fails completely. Most of the work described in this chapter was undertaken to circumvent these problems and to realize the potential promise of the synthesis. 

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