Synthetic chemistry with nitrous oxide and triazenes

Nitrous oxide (N2O) has gained much interest because of its physiological effects ("laughing gas") and its negative environmental impact ("greenhouse gas", "ozone-depleting substance"): It has a lifetime of more than 100 years in the atmosphere. Its persistent character shows how challenging it is to convert N2O into more valuable products. From a synthetic point of view, N2O has potential as diazo (N2) transfer reagent, but applications in synthetic organic chemistry are scarce. The main challenges are to capture N2O, avoid the loss of N2, and to overcome poor-selectivity and -yields. Herein, we describe two examples of the incorporation of two nitrogen atoms into the final product. Firstly, we use N2O as diazo transfer reagent in the preparation of triazolopyridines, which are valuable starting materials for heterocyclic compounds. The reactions can be performed under mild conditions and give synthetically interesting triazoles in moderate to good yields. Secondly, general methods to N1 acylated triazenes were missing previously. We developed routes to 1-acyl triazenes via acid-catalyzed hydration, or by gold- or iodine-catalyzed oxidation of 1-alkynyl triazenes. The latter compounds are prepared from N2O. The properties of the N1 acylated triazenes are distinct compared to other triazenes, displaying different physical and chemical properties. Under strong acidic conditions, 1-acyl triazenes act as acylation reagents. Finally, despite that triazene chemistry is known for more than 160 years, the preferred coordination site of acids still remained a matter of debate (N1, N2, or N3). In search of experimental evidence, we have analyzed triflic acid, B(C6F5)3, and PdCl2 adducts of triazenes by IR, NMR spectroscopy and single crystal X-ray crystallography. For all cases, we found the acid coordinating to the N1 atom of the triazene. This preference should be taken into account for future acid- and transition metal-catalyzed reactions with triazenes. Altogether, this thesis contributes to triazene chemistry and synthetic chemistry with N2O. In this way, we provide further evidence that N2O can be used as a diazo donor to get to synthetically interesting N-containing products.