Application of Glaser-Hay Diyne Coupling To Constrain Nα-Amino Acid Amides via a N-N Bridge.

We present the application of a Glaser-Hay diyne coupling for the synthesis of conformationally constrained Nα-amino acid amides with different diyne ring sizes. Twelve-membered rings were the smallest rings that could be prepared by this approach. We observed the formation of triethylammonium adducts in the cases of smaller (10- and 11-membered) rings. Calculation of the conformational barriers for the cyclization reactions of various ring sizes demonstrated that the formation of amino acid-derived smaller rings by this reaction is thermodynamically unfavorable.