Click chemistry, a term used to describe a number of high yield reactions, is used far and wide by chemists.  The azide alkyne Huisgen cycloaddition typifies click chemistry and awhile back, I described it as my favorite reaction.  In my heartfelt description of my favorite reaction, I described some recent research reported in Nature about an “unclick” reaction.  Having an unclick reaction opened up many new options for click chemistry and was a very exciting development for the field.  Unfortunately, doubts are now surfacing as to the validity of this research.  Bethany Halford at Chemical and Engineering News has written a great summary of the controversy.