Construction of the 4-Azafluorenone Core in a Single Operation and Synthesis of Onychine

Abstract

This study describes the synthesis of the 4azafluorenone core in a single operation using readily available starting materials. Condensation of an amidrazone with ninhydrin intercepts an intermediate 1,2,4-triazine derivative, which engages norbornadiene in a merged [4 + 2]/bis-retro[4 + 2] sequence to deliver the azafluorenone core. The tricyclic core established in this manner was elaborated to onychine, the simplest natural product in the 4-azafluorenone alkaloid family. Scheme 2. Synthesis of 1,2,4-Triazine and 4-Azafluorenone Core Scheme 3. One Step Construction of 4-Azafluorenone Core and Elaboration to Onychine