Diazo transfer to 1,3-dicarbonyl with tosyl azide

[![Reaction scheme](https://i.stack.imgur.com/5oqiw.png)](https://i.stack.imgur.com/5oqiw.png)


What is the mechanism for the above reaction? 




This starting material is not actually an enone; it is a 1,3-dicarbonyl, confusingly drawn as the enol tautomer. 1,3-Dicarbonyls are mildly acidic ($\mathrm pK\_\mathrm a \sim 10$) and can be deprotonated by weak bases, such as triethylamine ($\mathrm pK\_\mathrm a \sim 9$), which was mentioned in the question. So, now, we have an enolate ion which is *nucleophilic*.


Tosyl azide, $\ce{TsN3}$, is an odd reagent. It's easy to think that it is acting as a nucleophile of some sort, because the azide ion is nucleophilic, but actually it is an *electrophile*.


[![Mechanism - part 1](https://i.stack.imgur.com/hoiYm.png)](https://i.stack.imgur.com/hoiYm.png)


The next part is the removal of the formyl group, which is a bit tricky. Here I am not 100% sure, so take it with a pinch of salt, but I think Mith was on the right track with the retro-(3+2) cycloaddition. This is my guess:


[![Mechanism - part 2](https://i.stack.imgur.com/W6h6c.png)](https://i.stack.imgur.com/W6h6c.png)


In fact, the cyclisation of the terminal nitrogen onto a carbonyl group has been proposed before, in mechanistic studies of electrophilic azidation by D. A. Evans.1 That makes me feel a bit more confident in my guess!


[![Proposed triazoline formation](https://i.stack.imgur.com/75cB1.png)](https://i.stack.imgur.com/75cB1.png)


Anyway, the product above is simply a resonance form of the diazo product you want.


[![Mechanism - part 3](https://i.stack.imgur.com/PPQxU.png)](https://i.stack.imgur.com/PPQxU.png)




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**Reference**


1. Evans, D. A.; Britton, T. C.; Ellman, J. A.; Dorow, R. L. The asymmetric synthesis of α-amino acids. Electrophilic azidation of chiral imide enolates, a practical approach to the synthesis of (*R*)- and (*S*)-α-azido carboxylic acids. *J. Am. Chem. Soc.* **1990,** *112* (10), 4011–4030. [DOI: 10.1021/ja00166a045](https://doi.org/10.1021/ja00166a045). Non-paywall version available from the [Evans group website](http://evans.rc.fas.harvard.edu/pdf/evans126.pdf).


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