Exploitation of a Tuned Oxidation with <i>N</i>-Haloimides in the Synthesis of Caulibugulones A–D
作者:Fabrício F. Naciuk、Julio C. Milan、Almir Andreão、Paulo C. M. L. Miranda
DOI:10.1021/jo302772t
日期:2013.5.17
Marine alkaloids caulibugulones A-D were synthesized in six steps starting from the readily available 2,5-dimethoxybenzaldehyde. Pomeranz-Fritsch reaction of N-(2,S-dimethoxybenzyl)-N-(2,2-dimethoxyethyl)-2-nitrobenzenesulfonamide proceeded smoothly to give 5,8-dimethoxyisoquinoline, which was oxidized to isoquinolinadiones by a tunable oxidation reaction with N-haloimides. Therefore, NBS furnished direct conversion to the isoquinoline-5,8-dione; alternatively, N-haloimides of cyanuric acid provided both oxidation and halogenation generating 6,7-dihaloisoquinoline-5,8-diones. Aminolyses of these isoquinolinediones with methylamine or ethanolamine produced the isoquinolinedione alkaloids caulibugulones A-D in 24-57% overall yield.