[Nescafe]

Hi,

Does anyone know how the zinc catalyzes this 1,3 dipolar cycloaddition? My guess would be that the zinc coordinates to the dipolarophile (nitrile) and reduces its electron density therefore making it more susceptible to an attack by the azide but I am uncertain.

http://pubs.acs.org/doi/abs/10.1021/jo010635w

Thanks,

Nescafe.

[NotExactly]

Hi Nescafe,

Given your pervious post on triazole synthesis, it seems like you are preparing a review of Sharpless Click chemistry! 

The Zinc defintiely does act as a Lewis acid catalyst but in the paper Sharpless writes "Our
mechanistic studies to date imply that the role of zinc is not simply that of a Lewis acid; a number of other Lewisacids were tested and caused little to no acceleration of the reaction.23 In contrast, Zn2+ exhibited a 10-fold rateacceleration at 0.03 M, which corresponds to a rate
acceleration of approximately 300 at the concentrations typically used. The exact role of zinc is not yet clear."

The fact that they need 50 mol% Zinc is a little suspicious in my opinion.  Maybe the fact that it is a divalent cation is important.