Catalyzed reaction of dimethyl diazomalonate with 2-alkenylthiophenes
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The reaction of 2-alkenylthiophenes with dimethyl diazomalonate (DMDM) in the presence of CuCl or Rh(OAc)2 has been studied, and it has been found that the course of the reaction is determined by the reaction conditions and the structure of the alkenylthiophene (the presence of substituents in the 2-alkenyl group and the 5-position of the thiophene ring).
In the thermocatalytic decomposition of DMDM in the presence of CuCl, 2-alkenylthiophenes afford the products of the addition of bismethoxycarbonylcarbene at the exocyclic double bond, and of insertion into theα-C-H bond of the thiophene ring.
The formation has been observed for the first time of stable thiophenonium ylides from 2-propenyl- and 2-isobutenylthiophene and DMDM during the catalyzed decomposition of the latter in the presence of Rh(OAc)2 at 20‡C.
The possibility has been shown of the ylides formed participating in inter- and intra-molecular transfer of the bismethoxycarbonylcarbene fragment to form the corresponding products of cyclopropanation at the C=C bond or of insertion at the C-H bond.
Total stereoselectivity is shown in the formation of 2-thienylcyclopropanedicarboxylate esters either from the ylides, or from the appropriate 2-alkenylthiophenes and DMDM when the latter undergoes catalyzed decomposition.
It is suggested that ylides are formed as intermediates in the reactions of alkenyl substituted furans and thiophenes with carbenes.
KeywordsEster Dimethyl Double Bond Carbene Thiophene
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