Catalytic cross coupling reactions

Transistion metal catalyzed cross coupling reactions are among the most versatile methods for establishing new carbon-carbon bonds. Nevertheless, (Csp3-Csp2) coupling features several synthetic problems i.e. the correct choice of the nature of electrophile and nucleophile or the appearance of homocoupling products. In this work Kumada type cross coupling reactions of alkyl Grignard reagents with different types of aromatic electrophiles were investigated. Transition metal compounds of the general formula {MCl2[Ph2P(CH2)1-3PPh2]} (M = Pd, Ni, Fe) are versatile precatalysts for the coupling of cyclohexyl Grignard reagents with either fluorinated bromobenzene or bromothiophene derivatives, catalytic activity of the precatalysts depends on the diphosphane ligands and increases in the order dppm < dppe < dppp, if cyclohexyl Grignard solutions without any additives are used, the catalytic activity of the precatalysts depends on the transition metal and increases in the order Fe < Ni < Pd. The addition of lithium salts to the Grignard solutions leads to an enhancement of activity for all precatalysts. The effect is most pronounced for iron precatalysts which upon addition of LiBr show an activity that is well comparable to that of palladium complexes under the same reaction conditions

Merging Visible-Light-Photoredox and Nickel Catalysis

A new combination: The merging of visible‐light‐photoredox catalysis and nickel catalysis has been successfully achieved for cross‐coupling reactions. The synthetic scope and limitations of the combination of nickel and photoredox catalysis for Csp3-Csp2 cross‐coupling reactions is discussed

Configurationally stable, enantioenriched organometallic nucleophiles in stereospecific Pd-catalyzed cross-coupling reactions: an alternative approach to asymmetric synthesis

Several research groups have recently developed methods to employ configurationally stable, enantioenriched organometallic nucleophiles in stereospecific Pd-catalyzed cross-coupling reactions. By establishing the absolute configuration of a chiral alkyltin or alkylboron nucleophile prior to its use in cross-coupling reactions, new stereogenic centers may be rapidly and reliably generated with preservation of the known initial stereochemistry. While this area of research is still in its infancy, such stereospecific cross-coupling reactions may emerge as simple, general methods to access diverse, optically active products from common enantioenriched organometallic building blocks. This minireview highlights recent progress towards the development of general, stereospecific Pd-catalyzed crosscoupling reactions using configurationally stable organometallic nucleophiles

Oxidative coupling reactions of pyridine

Abstract available: p.i

Synthesis of 1 alpha,25-Dihydroxyvitamin D Analogues Featuring a S-2-symmetric CD-ring Core

Three analogues of 1 alpha,25-dihydroxyvitamin D-3 (calcitriol), featuring a transfused decalin C, D-core with local S-2-symmetry, and possessing identical side-chain and seco-B,A-ring structures, have been synthesized starting from readily available (4aR, 8aS)octahydronaphthalene-1,5-dione(7). The very short sequences involve the simultaneous introduction of the side-chain and seco-B, A-ring fragments via Suzuki and Sonogashira coupling reactions. The analogues are devoid of relevant biological activity

Nickel-Catalyzed Enantioselective Reductive Cross-Coupling Reactions

Nickel-catalyzed reductive cross-coupling reactions have emerged as powerful methods to join two electrophiles. These reactions have proven particularly useful for the coupling of sec-alkyl electrophiles to form stereogenic centers; however, the development of enantioselective variants remains challenging. In this Perspective, we summarize the progress that has been made toward Ni-catalyzed enantioselective reductive cross-coupling reactions

Silver-Mediated Decarboxylation Reactions: Expanding Reaction Scope through Kinetic Analysis

Transition metal-catalyzed decarboxylative coupling reactions have received considerable attention in recent years as a method to obtain biaryl compounds. However, the oxidative version of this reaction class is still in its infancy, limited to specific substitution patterns on the benzoic acids – ortho-substitution - used in these transformations. This thesis describes our attempts to understand the key decarboxylation step of this important class of reactions. The first chapter of this thesis discusses an introduction into cross-coupling reactions, decarboxylative cross-coupling reactions, and outlines relevant physical organic parameters. The following chapter details the synthesis of a series of (1,10-phenanthroline)silver(benzoate) complexes. This chapter also describes their usage in the development of a model of the decarboxylation of the (phen)Ag(benzoate) complexes enabling the prediction of new benzoic acids to be used in oxidative decarboxylative coupling reactions. The last chapter discusses our recent progress on the extension of our decarboxylation methodology to silver heteroaromatic acid carboxylates. This final chapter also describes our preliminary attempts to correlate the rates of decarboxylation of Ag(heteroaromatic carboxylate) complexes with various electronic parameters

Novel Fmoc-Polyamino Acids for Solid-Phase Synthesis of Defined Polyamidoamines

A versatile solid-phase approach to sequence-defined polyamidoamines was developed. Four different Fmoc-polyamino acid building blocks were synthesized by selective protection of symmetrical oligoethylenimine precursors followed by introduction of a carboxylic acid handle using cyclic anhydrides and subsequent Fmoc-protection. The novel Fmoc-polyamino acids were used to construct polyamidoamines demonstrating complete compatibility to standard Fmoc reaction conditions. The straightforward synthesis of the building blocks and the high efficiency of the solid-phase coupling reactions allow the versatile synthesis of defined polycations