Methyl cyanoacetate → methyl (2Z)-(5-chloro-2-oxo-1,2-dihydro-3H-indol-3-ylidene)(cyano)acetate

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Reaction Steps

A stirred mixture of 5-chloro-1H-indole-2,3-dione, starting material VIII, (90.8 g, 0.5 mol) and methyl cyanoacetate (44.1 ml, 0.5 mol) in methanol (1000 ml) was treated with piperidine (2 ml) and heated under reflux for 5 hours before standing overnight at ambient temperature. The crude (5-chloro-2-oxo-1,2-dihydro-indol-3-ylidene)-cyanoacetic acid methyl ester was removed by filtration, washed with cold methanol (2×150 ml) and dried in vacuo to give 117.6 g (90%) of a dark purple solid. This was a 6.5:1 mixture of geometric isomers which was sufficiently pure by 1H NMR for subsequent reaction.

Provenance & Evidence