Ring‐Expansion Reaction of Isatins with Ethyl Diazoacetate Catalyzed by Dirhodium(II)/DBU Metal‐Organic System: En Route to viridicatin (cas 129-24-8) Alkaloids

Add time:09/25/2019    Source:infona.pl

We present here the NHC‐dirhodium(II)/DBU‐catalyzed ring expansion reaction of isatins with ethyl diazoacetate. This new one‐pot protocol yields the ethyl 3‐hydroxy‐2(1H)‐oxoquinoline‐4‐carboxylate core, regioselectively and in good to excellent yields. A DFT mechanistic study indicates metallocarbene formation between the 3‐hydroxyindole‐diazo intermediate and the dirhodium(II) complex to be the rate‐limiting step of the reaction. The synthesized ethyl 3‐hydroxy‐2(1H)‐oxoquinoline‐4‐carboxylate core could be readily converted to viridicatin (cas 129-24-8) alkaloids, in yields up to 80 % by a microwave‐assisted Suzuki–Miyaura cross coupling of the 3‐hydroxy‐4‐bromoquinolin‐2(1H)‐one with arylboronic acid.

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