Stereoselective synthesis of alkenes via base-metal-catalyzed addition reactions to alkynes and activation of hydrogen peroxide and carbon dioxide by iron complexes

Abstract

Alkene functionality can be found in the majority of natural products, drugs, catalysts and organic materials. Therefore, methods of C-C double bond formation constitute a cornerstone of organic synthesis. Selective formation of either (Z)- or (E)-isomer is especially desirable. 1,2-Addition to alkynes unites a large arsenal of methods of C-C double bond formation, among which the addition of carbon-centered species is the most interesting, since it offers a possibility of construction of the carbon skeleton. The first part of the present dissertation is devoted to the development of methods of selective addition of carbon reagents to alkynes. Chapter 1 reviews the existing methods of addition of carbon-centered species, generated from organometallic reagents, organic halides or carbonyl compounds to C-C triple bond with the accent on their stereoselectivity. Carbometalative mechanisms lay in the background of the majority of the reactions in this chemistry. The Z/E selectivity of 1,2-addition to triple bond can be controlled via predominance of either syn- or anti-addition or via Z/E isomerization of the addition intermediates. In Chapter 2 a novel method of disubstituted alkene synthesis via reductive addition of alkyl halides to terminal arylalkynes is described. The remarkable feature of this method is highly selective formation of (Z)-alkenes (generally Z/E > 10:1). Minor modifications of the reducing agent allowed the extension of the substrate scope to the primary alkyl iodides. Mechanistic studies revealed that this reaction proceeds as a formal anti-carbozincation. The resulting organozinc species form disubstituted (Z)-alkenes upon aqueous work-up. On the other hand, it would be interesting to utilize these species in cross-coupling reactions to allow the selective synthesis of trisubstituted alkenes. In Chapter 3 a catalytic system for highly regioselective copper-catalyzed allylation of these reagents is described. In Chapter 4 the results on stereoselective intermolecular addition of aldehydes and ketones to alkynes in the presence of zinc and trimethylchlorosilane are summarized. This reaction gives 1-chloro-1,3-dienes as products. The activation of small molecules has become an increasingly attractive area of research over the last years. In Chapter 5 an outline is given of the literature examples of small-molecule activation, namely activation of carbon dioxide and hydrogen peroxide, by iron complexes. In Chapter 6 the studies on small-molecule activation by iron-sulfur cubane clusters are presented. Electrochemical reduction of carbon dioxide and hydrogenation of alkenes were studied. As an additional result, synthesis and characterization of an unprecedented organic iron(I) ate-complex is reported. Structural modification of a non-heme iron complex with hydrogen-bond-donating substituents is described in Chapter 7. The deep impact of these modifications on the structure and reactivity of the resulting complex is discussed.