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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: JakeG on January 14, 2020, 03:22:52 PM

Title: Bromination of a Bis(thiadiazole)
Post by: JakeG on January 14, 2020, 03:22:52 PM

First time posting.

I have been having issues with brominating the thiadiazole shown in attached picture. The target has been reported before, but it seems that the authors have not provided a thorough description of the procedure (other than HBr, Br₂).


The side product that I have isolated is also in the picture. Ideally a 1-step procedure would be great (:P)
Useful info, the overall molecule has a "low degree" of aromaticity, so rearomatisation isn't a super strong driving force.

Title: Re: Bromination of a Bis(thiadiazole)
Post by: wildfyr on January 14, 2020, 05:00:02 PM

Do they specify reflux? Perhaps it should be done cold or RT.

Title: Re: Bromination of a Bis(thiadiazole)
Post by: pgk on January 15, 2020, 12:16:08 PM

You can treat your isolated product with 2,3‐dichloro‐5,6‐dicyano‐p‐benzoquinone (DDQ), in order to obtain the desired aromatic product. But pay attention during extractions with an acidic aqueous medium because DDQ liberates HCN during acid hydolysis (work in the hood and appropriately treat the reaction waste waters).
1). Stereochemistry of Dehydrogenation of 1,4,‐Cyclohexadiene with 2,3‐Dichloro‐5,6‐dicyano‐p‐benzoquinone, Helvetica Chimica Acta, 67(1), 105-112, (1984)
https://onlinelibrary.wiley.com/doi/abs/10.1002/hlca.19840670113
2). Old reagents, new results: Aromatization of Hantzsch 1,4-dihydropyridines with manganese dioxide and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone, Tetrahedron, 51(23), 6511-6516, (1995)
https://www.sciencedirect.com/science/article/abs/pii/0040402095003183

Title: Re: Bromination of a Bis(thiadiazole)
Post by: JakeG on January 16, 2020, 03:06:58 AM

Thank you both for the useful answers. I will give both a shot today and will let you know if I am successful.

Fingers crossed :)