ON THE MECHANISM OF THE REDUCTION OF 1-PHENYL-3-(4-PYRIDINYLMETHYLENE)-2-OXINDOLE WITH SODIUM-BOROHYDRIDE IN METHANOL

Sodium borohydride reduction of 1-phenyl-3(4-pyridinylmethylene)-2-oxi ndole 1 in methanol gives a high yield of the oxindole 2, a precursor to linopirdine. The reduction is accelerated by methanol and the major by-products during this reduction are the diastereomeric Michael addu cts between 1 and 2 and the overreduced products, 9 and 11. Surprising ly, indole 9 is not derived from further reduction of 2 but is formed concurrently, whereas the ring opened product 11 is the unexpected red uction product derived from 2.