Chemical Transformation of Protoberberines. IV. A Novel, Simple Synthesis of (±)-Canadaline and a Retroproto-berberine from Tetrahydroberberine

Abstract

Heating of tetrahydroberberine (1) in ethyl chloroformate preferentially afforded the C₈-N bond cleavage (4) with small amounts of the C₆-N and C₁4-N bond cleavage products (5 and 6, respectively). The urethane (4) was effectively converted to (±)-canadaline (2), a secoberbine alkaloid, and a retroprotoberberine (3).