[nox]

I refer you to this OrgSyn prep: http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv1p0327

Mechanism of the second step I can figure out just fine, but the first step eludes me.

All I have up to this point is that chloral hydrate probably reverts to trichloroacetaldehyde in solution, which condenses with aniline to form the imine presumably. But how you tack on the carbonyl groups is beyond me. Going haloform on the imine would give you N-formylaniline + chloroform. So you would install the first carbonyl but that just seems like a dead end to me.

[Honclbrif]

With the mechanism I've drawn, none of the carbons originating from chloral hydrate change their oxidation state. Nor is there any breakage of carbon-carbon bonds. Think neighboring group participation.

[nox]

Ah I see. Figured it had something to do with the CCl3 group. Seems it bears some mechanistic similarity to the Reimer-Tiemann reaction, at least in terms of how chloroform gets transformed into a formyl group.

[Åke]

You might want to check: The Chemistry of Isatins: a Review from 1975 to 1999 J. Braz. Chem. Soc., Vol. 12, No. 3, 273-324, 2001.

The article is available free of charge: http://jbcs.sbq.org.br/jbcs/2001/vol12_n3/187-00.pdf 

Regards,

Vedran