Magnesium Ion Assisted Highly Regio- and Chemoselective Reduction of 5H-Pyrrolo[3,4-b]pyridine-5,7(6H)-diones with Sodium Borohydride. A Convenient Synthesis of 6,7-Dihydro-7-hydroxy-5H-pyrrolo[3,4-b]pyridin-5-ones

Abstract

Abstract 6-Substituted and unsubstituted 6,7-dihydro-7-hydroxy-5H-pyrrolo[3,4-b]pyridin-5-ones were predominantly obtained in excellent yield by the reduction of the corresponding 5,7-diones with sodium borohydride in the presence of Mg ion at 0 °C. The highly regioselective production of the 7-hydroxy lactam in preference to the 5-hydroxy isomer was reasonably interpreted in terms of a chelate complex formation between the dione and Mg ion. The regioisomeric assignment was achieved by the transformation of the 7-hydroxy lactam to 2-(hydroxymethyl)-3-pyridinecarboxamides which could be converted to the known azaphthalide, furo[3,4-b]pyridin-5(7H)-one. Furthermore, the high chemoselectivity was found to be retained below 0 °C to give the partial reduction product, hydroxy lactam, exclusively.