SYNTHESIS OF ISO- NORISO- AND DESETHYLTUBOFLAVINE

Treatment of 4,5 ‐dihydrocanthin‐6‐one (V) (prepared from synthetic canthinone (IV)) with ethyl or methyl magnesium iodide and methanolic hydrochloric acid yielded the ethyl or methyl compounds VI and IX. Oxidation of the latter compounds with selenium dioxide in dimethylformamide gave rise to the Pleiocarpa alkaloids isotuboflavine (II) and norisotuboflavine (III) in low yields. Deethyltuboflavine (VIII) was isolated as a byproduct from further oxidation of norisotuboflavine. Copyright © 1968 Verlag GmbH & Co. KGaA, Weinheim