Last December, Dr. Steve Ritter of the Chemical and Engineering News asked me to comment on a paper from the lab of Prof. Petr Beier of the Czech Academy of Sciences. I gladly did (http://cen.acs.org/articles/94/web/2016/12/Fluorinated-azides-click-make-triazoles.html?type=paidArticleContent) and I just want to share my thoughts with you in the event you have not seen the Beier paper.
Every now and then we need a reminder of a rather straightforward kind: if we have trouble making a bond, just reverse the darn polarity of reagents! It is remarkable how infrequently this way of thinking pops into our heads, and I am judging from years of experience. Indeed, unless you are into radical reactions, there are always at least two ways to make a bond by a polar mechanism. In the example described by the Prague team in the Angewandte article, the curious CF3N3 molecule was the target. Attempts to forge the C-N bond using CF3I as the electrophile led nowhere, whereas using the fluoroalkyl portion as the nucleophile delivered CF3N3 and other uncommon azides without a glitch. I know this stuff ultimately relates to the well-known umpolung arguments, but those of us who are in the business of making bonds would still rather search “closer to the lamp post” than reverse reagent polarity. I am convinced that there are a lot of other previously “unmakable” molecules that might be made using this simple logic. We should keep this in mind.