Potassium nitrosodisulfonate quinone synthesis

In addition to the aforementioned syntheses of various carbazole-l,4-quinone alkaloids, many formal syntheses for this class of carbazole alkaloids were also reported. These syntheses involve the oxidation of the appropriate 1- or 4-oxygenated-3-methylcarbazoles using Fremy s salt (potassium nitrosodisulfonate), or PCC (pyridinium chlorochromate), or Phl(OCCXI F3)2 [bis(trifluoroacetoxy)iodo]-benzene. Our iron-mediated formal synthesis of murrayaquinone A (107) was achieved starting from murrayafoline A (7) (see Scheme 5.34). Cleavage of the methyl ether in murrayafoline A (7) and subsequent oxidation of the resulting intermediate hydroxycarbazole with Fremy s salt provided murrayaquinone A (107) (574,632) (Scheme 5.113). 

Ellipticine (E) 1 is an indolic alkaloid with antitumor activity. Some of its phenolic derivatives as N-methyl-9-hydroxyellipticine (Celiptinium), obtained from 9-hydroxy ellipticine (9-OH E), exhibit high cytotoxicity. 38 Syntheses of 9-OH E are not satisfactory considering yields and cost, justifying the attempts at the direct conversion of E to 9-OH E via 9-oxoellipticine (9-0X0 E). Potassium nitrosodisulfonate (Fremy s salt), a valuable oxidant for the synthesis of quinone-imine from heterocyclic amines,139 was used. Under these conditions the conversion of E to 9-0X0 E was observed for the first time. Its reduction to 9-OH E is then easily achieved with ascorbic acid. The radical nature of Fremy s salt [ 0-N(S03K)2] led us to carry out the oxidation reaction under sonication in order to increase the yields via an easier electron transfer.1 1... 

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