Disulfoxide Ligands in Rhodium Catalyzed Asymmetric 1,4-Addition: First Studies and Future Directions

Disulfoxides with atropisomeric backbones are introduced as readily available chiral ligands for the rhodium-catalyzed 1,4-addition of arylboronic acids to unsaturated carbonyl compounds. The ligands are obtained in pure form from either commercially available or easily synthesized starting materials. Precatalysts with general formula {(disulfoxide)RhCl}2 were prepared in high yield and were fully characterized. Preliminary results on the influence of steric and electronic modifications of the ligand structure and their impact on the catalytic behavior are presented

New N-heterocyclic carbene ligands and their applications in homogenous catalysis

Die Entwicklung von N-heterozyklischen Carbenen (NHCs) als Liganden für Übergangsmetallkatalysatoren hat zu vielen neuen Errungenschaften in der homogenen Katalyse beigetragen. Um die Familie von unterschiedlichen NHC Liganden zu erweitern, werden in der vorliegenden Dissertation folgende Ergebnisse präsentiert: (1) Eine Klasse von gesättigten NHC Liganden mit Naphthyl-basierten Seitenketten und ihre gute Performenz in drei unterschiedlichen katalytischen Reaktionen, und (2) eine Reihe von chiralen NHC Liganden, welche aus C2-symmetrischen Diaminen mit Naphthylseitenketten dargestellt wurden, sowie die erfolgreiche Anwendung der entsprechenden Palladiumkomplexe in der asymmetrischen Synthese von Oxindolen mit quaternären Kohlenstoffzentren. Das zweite Kapitel beschreibt die Synthese und Charakterisierung von leicht zugänglichen und stabilen NHCs, die mit Naphthyl in der Seitenkette substituiert sind. Bei der Anwendung in der Katalyse wurden exzellente Resultate in Palladium- basierten Kupplungsreaktionen, in der Ruthenium-basierten Metathese sowie in der organokatalytischen Ringöffnungsalkylierung von Epoxiden erhalten. Im dritten Kapitel wurde die Untersuchung der NHCs zum entsprechenden chiralen Gegenstück ausgeweitet indem die Chiralität von C2-symmetrischen Diaminen für das heterozyklische Rückgrat genutzt wurde. Die zugehörigen Palladiumkomplexe mit diastereomerenreinen NHC Liganden wurden aufgetrennt und in der asymmetrischen Synthese von 3-Aryl-3-methyl-oxindolen getestet. Hierbei zeigten die katalytischen Daten einen drastischen Einfluss auf die Enantioselektivität je nach der Orientierung der Seitenkette. Das vierte Kapitel befasst sich mit einem anderen ähnlichen NHC Liganden, der die asymmetrische Synthese von 3-Allyl-3-aryl-oxindolen mit einer hohen Chemo- und Enantioselektivität begünstigen konnte. The recent development of N-heterocyclic carbenes (NHCs) as ligands for transition metal catalysts has proved to be very fruitful in the field of homogeneous catalysis. In order to expand the family of versatile NHC systems for catalysis, this dissertation presents: (1) a class of saturated NHC ligands with naphthyl-derived side chains and their good performance in three different types of catalysis, and (2) a series of chiral NHC ligands derived from C2-symmetric diamines with naphthyl side chains and the successful applications of their palladium complexes in the asymmetric synthesis of oxindoles bearing quaternary carbon centers. Chapter 2 describes the synthesis and characterization of a new class of easily accessible and stable NHCs which incorporate substituted naphthyl side chains. In catalysis, excellent catalytic results are obtained in palladium-based coupling reactions, in ruthenium-based metathesis, and in the organocatalytic ring-opening alkylation of epoxide. In Chapter 3, the NHC study was expanded to their chiral counterparts by introducing the chiral regime of C2-symmetric diamines into their heterocyclic backbone. Palladium complexes bearing diastereomerically pure NHC ligand were separated and tested in the asymmetric synthesis of 3-aryl-3-methyl- oxindoles. The catalytic data demonstrates the dramatic effects on enantioselectivity according to the orientation of the side chains. Chapter 4 addresses another similar chiral NHC ligand which could promote the asymmetric synthesis of 3-allyl-3-aryl- oxindoles with high chemo- and enantioselectivity

Regiospecific Ficini [2 + 2] Cycloaddition of Ynamides with Cyclic Isoimidium Salts under Catalyst-Free Conditions

The regiospecific [2 + 2] cycloaddition of cyclic isoimidium salts with ynamides is described. This effort led to the development of the first successful example of a catalyst-free, thermally driven Ficini [2 + 2] cycloaddition process of ynamides with α,β-unsaturated carbonyl compounds, giving the stable cyclobutenamides in excellent yields (up to 99%)

Regiospecific Ficini [2 + 2] Cycloaddition of Ynamides with Cyclic Isoimidium Salts under Catalyst-Free Conditions

The regiospecific [2 + 2] cycloaddition of cyclic isoimidium salts with ynamides is described. This effort led to the development of the first successful example of a catalyst-free, thermally driven Ficini [2 + 2] cycloaddition process of ynamides with α,β-unsaturated carbonyl compounds, giving the stable cyclobutenamides in excellent yields (up to 99%)

Diastereoselective Synthesis of Dibenzo[<i>b</i>,<i>d</i>]azepines by Pd(II)-Catalyzed [5 + 2] Annulation of <i>o</i>‑Arylanilines with Dienes

An efficient method for the construction of dibenzo­[<i>b</i>,<i>d</i>]­azepines containing two distinct stereogenic elements in a highly diastereoselective fashion is described. The key of the [5 + 2] reaction is to form a π-allylpalladium species through sequential C–H activation and regiospecific migratory insertion of the diene. This observation contrasts with the behavior of 1,2-alkenes that generally underwent direct alkenylation via β-hydride elimination

Pd(0)-Catalyzed Intermolecular Dearomatizing [3 + 2] Spiroannulation of Phenol-Based Biaryls and Allenes

Readily available phenol-derived biaryls reacted with allenes under palladium catalysis to provide a variety of highly valuable spiro­[cyclohexane-1,1′-indene]-2,5-dien-4-ones. This new catalytic process, involving a key step of regioselective allylative dearomatization of phenol, proceeded efficiently through a [3 + 2] spiroannulation pathway by overcoming undesired β-hydride elimination. Preliminary asymmetric studies showed that high enantioselectivity could be realized by using a commercially available PHOX ligand. Moreover, the potential application of this method was exemplified by several further transformations

Catalytic Enantioselective Tautomerization of Metastable Enamines

The first example of catalytic enantioselective tautomerization of structurally labile but isolable enamines for accessing their chiral imine-tautomers is described. Kinetically stable enamine-based dibenzo­[<i>b</i>,<i>d</i>]­azepines were tautomerized by a simple chiral BINOL–phosphoric acid, providing a variety of seven-membered imine products bearing both central and axial stereogenic elements in good yields (up to 96%) with excellent enantio- and diastereoselectivities (up to 97% ee, >20:1 dr)

Highly Chemo- and Regioselective Construction of Spirocarbocycles by a Pd(0)-Catalyzed Dearomatization of Phenol-Based Biaryls with 1,3-Dienes

A novel Pd(0)-catalyzed intermolecular carbocyclization of phenol-derived biaryls with 1,3-dienes has been implemented through a sequence of oxidative addition to the C–I bond, regioselective olefin insertion, and allylative dearomatization. This method provides a broad range of attractive spirocyclic compounds bearing two contiguous tertiary/quaternary carbon centers in good yields with excellent chemoselectivity and regioselectivity. Moreover, preliminary results indicate that asymmetric control of this process is feasible with chiral ligands