Synthesis of 1,2-Dihydroisoquinolines by a Modified Pomeranz-Fritsch Cyclization

J Org Chem. 2020 Jan 17;85(2):1062-1072. doi: 10.1021/acs.joc.9b02987. Epub 2020 Jan 2.

Abstract

Isoquinolines (IQs) and their derivatives are present in many natural products and biologically active small molecules. Herein, we report a modified procedure for the classical Pomeranz-Fritsch protocol, which expands the scope of 1,2-dihydroisoquinoline (DHIQ) products. 1,2-DHIQs are an attractive branch point for the synthesis of IQs, but because of their innate reactivity, they have remained difficult to prepare. We demonstrate that the Fujioka/Kita conditions, combining trimethylsiyltriflate (TMSOTf) and an amine base, activate dimethylacetals required for Pomeranz-Fritsch cyclization under sufficiently mild conditions to prepare a broad range of 1,2-DHIQ products. We also demonstrate the synthetic value of these DHIQs by further functionalization to either reduced tetrahydroisoquinoline (THIQ) or fully aromatized IQ natural products.

Publication types

  • Research Support, Non-U.S. Gov't