Development of Novel Methodology for the in situ Preparation of Halodiazo Compounds and Investigation of Reactivities of α-Onium Diazo Compounds

Abstract

Diazo compounds have great synthetic potential as versatile reagents in organic synthesis. The formation of Rh(II) carbenoids from diazo compounds allows the selective formation of C-C and C-heteroatom bonds and the introduction of functionality into organic molecules. The thermal stability of diazo compounds, however, varies and depends strongly on the substituents and diazo compounds which are substituted by electron donating heteroatoms in α-position are known to decompose readily. They represent, however, a highly desirable class of diazo compounds as to allow the introduction of additional functional groups into organic molecules for further transformations. The development of new methodology for the α-functionalization of diazo compounds and introduction of new functionality into diazo compounds under mild conditions, that allows their application in catalytic carbenoid chemistry, is therefore highly desirable. In Chapter 2, the development of a new methodology for the one-pot in situ electrophilic halogenation of diazophosphonates will be presented. The halodiazophosphonates could for the first time be applied in catalytic cyclopropanations with olefins. The methodology avoids the handling of potentially toxic α-metalated diazophosphonates and adds as a new convenient protocol to the preparation of diazo compounds. Parts of this chapter are published in Paper I. A different and complementary approach to halodiazo compounds will be presented in Chapter 3. Based on α-aryliodonium diazo triflate salts, we developed three new alternative methods for the in situ nucleophilic halogenations of diazoesters, diazophosphonates and diazopiperidinylamides and the halodiazo compounds were successfully used in Rh(II) catalyzed cyclopropanations with styrene or thermal intramolecular C-H insertion. The work of this chapter is published in Paper II. Chapter 4 deals with computational calculations of the transition states for the nucleophilic substitutions of the α-aryliodonium diazoester triflate salt with bromide, dimethylsulfide and triethylamine and gives an insight into the mechanism for the nucleophilic substitution reactions. The calculations were performed by Martin Hennum. Parts of this work are published in Paper II. Experimental kinetic measurements of thermal decompositions and substitution rates in Chapter 5 give an insight into the stabilities and reactivities of the α-onium diazo triflate salts and the effects of the substituents of the diazo compounds. Parts of this chapter are published in Paper II. Synthetic applications of the unexplored α-aryliodonium, α-dimethylsulfonium and α-triethylammonium diazo triflate salts will then be presented and discussed in Chapter 6 and a variety of interesting and unexpected reactivities of these compounds were discovered. The results presented in this chapter are unpublished.