A novel application of DDQ as electrophile in the Nenitzescu reaction

Reaction of 2,3-dichloro-5,6-dicyano-benzoquinone (DDQ) with secondary enaminones yields surprisingly 2-aza-spiro[4,5]decatrienes. The reaction occurs via cyclisation of the primary Michael-adduct with the nitrile group. Reaction of DDQ with tertiary and also certain secondary enamines leads to 3-amino-benzo[b]furan derivatives. This is formed not by Michael-addition, but via geminate radical ion pair formation with subsequent generation of an oxygen–carbon bond to yield benzofurans. The new products are investigated with regards to inhibition of purified human proteinkinase CK2 and their general cytostatic activity. It turned out, that the most active compound is the 3-amino-5-hydroxy-benzofuran derivative 11s with an IC50 value of 0,2 μM for CK2.

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