Matsumoto indole synthesis

Several workers have described Fischer indolization without the use of acidic catalysts, the epitome of green chemistry. These thermal syntheses are shown in Table 2 [66-68]. The first practical account of noncatalytic Fischer indole synthesis appears to be that of Fitzpatrick and Riser (entries 1-3) [66]. Matsumoto and colleagues have effected indolizations with p-toluenesulfonic acid in the absence of solvent at 250 C to afford indoles 1-4 from the corresponding ketones and phenylhydrazine hydrochlorides (Scheme 5) [69]. In some cases, ttichloroacetic acid was employed. 

Matsumoto, M., and Watanabe, N., Synthesis of 4-(cyanomethylidene)- and 4-(ethoxycarbonylmeth-ylidcnc)-4,5,6,7-lclrahydroindolcs and their dehydrogenation to 4-(cyanomethyl)- and 4-(ethoxycar-bonylmethyl)indoles. Heterocycles, 24, 2611, 1986. 

Matsumoto, M., Watanabe, N., and Ishida, Y, A facile synthesis of 4-(cyanomethyl)indoles and 4-(ethoxycarbonylmethyl)indoles from 5-halo-4-oxo-4,5,6,7-tetrahydroindolcs, Heterocycles, 24, 3157, 1986. 

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