83482-71-7Relevant articles and documents
Transformation of Indole Alkaloids. VI. A Novel Conversion of Oxindole Alkaloids into Indole Alkaloids via Indoline Derivatives
Yamanaka, Etsuji,Saito, Naoki,Suzuki, Yuko,Sakai, Shin-Ichiro
, p. 2068 - 2076 (2007/10/02)
Oxindole alkaloids chosen as starting materials were isopteropodine (1a) pteropodine (1b) isoformosanine (7a) and formosanine (7b).Reduction of the iminoethers prepared from the oxindole alkaloids with Et3O(1+)*BF4(1-), with NaBH3(OAc) or with NaBH4/SnCl4*2Et2O afforded the indoline derivatives (3a, 3b, 9a, 9b).The configuration at C7 of 3a, b was determined by NMR analysis of the N(a)-acetyl-N(b)-oxides (6a, b).The signals of H-14β were observed at high field (δ 0.5-1.0) owing to the shielding effect of the aromatic ring in all A type compounds studied.Oxidative conversion of the indolines to indole alkaloids was achieved by using MnO2 or Me2SO/(COCl)2/Et3N as oxidizing agents, and the latter reagent gave better results than the former.Tetrahydroalstonine (11) and akuammigine (12) were obtained from 3a, b, and 19-epiajmalicine (14) and 3-iso-19-epiajmalicine (15) from 9a, b.The A type compounds were more susceptible than the B type compounds to the present reduction and oxidation sequence.Keywords: transformation; oxindole alkaloids; indole alkaloids; heteroyohimbines; reduction; oxidation; dimethyl sulfoxide-oxalyl chloride; indoline