Selective Reduction of a cyclic di-imine species

Recently, I synthesized 2,4-Diphenyl-7,8-dimethyl-3H-1,5-benzodiazepine from Benzil and 4,5-dimethylphenylene-1,2-diamine. I was able to get around 1.0 gram (58% yield) from the synthesis and wanted to try some nitrogen chemistry with it.

My idea was to selectively, or methodically, reduce one of the two imines. However, due to the almost entirely equal nature of the imines, they both should be reduced via any of the main go-to's for reduction. My idea then was to try and reduce both nitrogens and then slectively protect one and then oxidize the other.

The problem i see here is that unless I can speedily acetylate one of the two nitrogens, i am bound to have a mixture of products.

Does anyone have any good literature on this, or at least maybe some words of wisdom regarding this?

PS: Something deep inside tells me this is a job for testing The borohydrides (cyano, triacetoxy, etc.), but I am not confident in my judgement.



The pictures above show the crashed out product from the synthesis. Melting point was as expected for literature.

Hmmm. I thought diazepines were 7 member rings, if you condense benzil with and 1,2-phenylenediamine won't you just get a six member quinoxaline. In your case you should get 2,3-diphenyl-6,7-dimethylquinoxaline! ad the heterocyclic nitrogens are identical since the molecue is symmetrical. Like this:-

Quote: Originally posted by Boffis

Hmmm. I thought diazepines were 7 member rings, if you condense benzil with and 1,2-phenylenediamine won't you just get a six member quinoxaline. In your case you should get 2,3-diphenyl-6,7-dimethylquinoxaline! ad the heterocyclic nitrogens are identical since the molecue is symmetrical. Like this:-

After running this at a larger scale, I was able to yield 58% (0.9909g) of the product. The crystals were ever so slightly tinged yellow/orange, but the crystals melt very close the literature value (found: 146-148C, lit: ~152C not shown in aforementioned paper). Below is some pictures of the actual crystals, which look different than they should for a 6-membered ring closure. I would expect some deeper coloration for the structure you proposed, or at least that's what my colleagues suggest.

CORRECTION