Oxygenation of indole derivatives tryptophan models

A special case of oxidative C=C bond cleavage with 0 is that 

This reaction is the initial step of the biosynthesis of the coenzyme nicotinamide-adenine dinucleotide (NAD) from tryptophan in mammals. 

There has been some controversy over the possible intermediates of this transformation. The oxo derivative 34 was once postulated as a biological intermediate, but later this was refuted as 34 was not metabolized to kynurenine [208]. Subsequently, it was shown that chemically 34 can be readily converted to kynurenine [209]. 

There have been numerous reports on catalyst systems that can mimic the action of tryptophan-2,3-dioxygenase. Indole derivatives have been used as substrates in most of these studies. 

In the Co(salen) catalyzed oxidative cleavage of 3-substituted indoles (35) to the corresponding o-formylaminophenyl ketone (36) in CH Cl at room temperature [210,211], the rate-determining step has 

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