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The first zinc-catalyzed one-step synthesis of quaternary propargylamines with four different substituents is described. The domino hydroamination-alkyne addition reaction gives access to functionalized propargylamines under mild conditions. Keywords: alkynes; domino reaction; hydroamination; metathesis; propargylamines; zinc The synthesis of fine chemicals and natural products is often a multistep process including salt-generating reactions. Nowadays the modern synthesis design demands for efficient techniques to minimize the number of steps towards the product and to avoid the formation of by-products. Domino and cascade reactions allow an ecologically and economically favourable synthesis. [1][2][3] These procedures describe closely coupled individual reactions that yield a product in a single process.The addition of an organic amine to C-C multiple bonds presents a challenging and demanding topic. The metal-catalyzed hydroamination has been studied with different types of catalysts. [4][5][6][7] We have reported the metal-catalyzed hydroamination reactions with a diversity of zinc complexes.[6] Hydroamination reactions of alkynes often resulted in the formation of unstable intermediates like enamines and imines and hence were reduced to the corresponding amines in a one-pot procedure. [7] Hydroaminations were also combined in a tandem process with several other reactions like Cope rearrangement, [8] hydroarylation, [9] hydrosilylation [10] and with diverse addition reactions. [11] We are interested in a combination of hydroamination and alkyne addition in a catalytic domino process yielding propargylamines. Such a sequence has not been described intensively and only a few cases are known. In the first report acetylene was converted in a copper-catalyzed reaction to propargyl-A C H T U N G T R E N N U N G amines having a secondary carbon center.[12] These copper-catalyzed reactions have been recently described with diverse phenylacetylenes.[13] The hydro-A C H T U N G T R E N N U N G amination leads to anti-Markovnikov products and the following alkyne addition thus yields a propargyl-A C H T U N G T R E N N U N G amine with a secondary carbon center. In case of a Zn/Cd catalyst the Markovnikov addition was observed but only propyne and dimethyl-or diethyl-A C H T U N G T R E N N U N G amine were used under drastic conditions.[14] Herein we describe a flexible zinc-catalyzed one-step synthesis of quaternary propargylamines with four different substituents. The reaction proceeds under mild conditions and tolerates different functional groups.During our studies on zinc-catalyzed hydroaminations we found that b-diiminate (BDI) complexes like 1 in presence of cocatalyst 2 lead to the catalytically active species 3 (Scheme 1). According to our results, the cocatalyst 2 protonates the precatalyst 1 irreversibly forming methane and generates the catalyst 3 as a cationic BDI-zinc complex with a low-coordinating triflate anion. We confirmed the molecular structure of 3·THF by single crystal X-ray diffraction...

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As ligand has it…︁ A new class of ruthenium catalyst based on a bioxazoline‐derived N‐heterocyclic carbene (IBioxNHC) ligand has been synthesized that exhibits high stability at elevated temperatures and is a suitable catalyst for olefin metathesis. A slow initiation rate, owing to the steric hindrance of the NHC ligand, may be of interest for certain metathesis applications.

IntroductionAlkene metathesis is well established as a valuable synthetic tool in organic chemistry, and has proven to be a unique technique for the construction of complex structures in a rapid and effective way [1]. Since all metathesis transformations (except diyne metathesis) can be promoted by the same carbene catalysts, it is possible to combine them in a sequential way and enable a metathesis cascade in one pot. A domino reaction has been defined as ''a process involving two or more bond-forming transformations which take place under the same reaction conditions without additional reagents and catalysts, and in which the subsequent reactions result as a consequence of the functionality formed in the previous step'' [2]. These domino processes, also called tandem, provide a tremendous increase in molecular complexity within the use of one single catalyst in one pot. By carefully adjusting the conditions and judicious choice of the catalytic complex, it is often possible to conduct the process with excellent regio-, chemo-, diastereo-, and even enantioselectivity. Domino processes are especially attractive not only because they provide elegance to the synthetic route but also for being ecologically and economically favorable since they minimize the amount of waste, solvents, reagents, and energy compared to stepwise reactions. Much effort has been invested in developing new methodologies involving metathesis domino processes that have been successfully applied to the preparation of biologically active and naturally occurring molecules. In this chapter, a selection of synthetic approaches with ruthenium-catalyzed domino reactions that include exclusively metathesis steps will be discussed, whereby syntheses involving tandem reactions connecting a metathesis reaction with a reaction of a different type [3] or several metathesis transformations occurring independently at the same time will not be described [4]. Through this collection of natural product syntheses, we would like to highlight the high efficiency and utility of metathesis domino reactions in organic synthesis, discuss its driving forces, limits, and scope, and ultimately illustrate the enormous synthetic potential of this transformation.

Metathesis reactions O 0286A Hexafluorobenzene-Promoted Ring-Closing Metathesis to Form Tetrasubstituted Olefins. -The solvent shows an unexpected promoting effect on the Ru-catalyzed ring-closing metathesis of a variety of substrates. Even electron-deficient olefins are converted into tetrasubstituted cyclic products in high yields and short reaction times. -(ROST, D.; PORTA, M.; GESSLER, S.; BLECHERT*, S.; Tetrahedron Lett. 49 (2008) 41, 5968-5971; Inst.

Review: 68 refs.

Synthesis of a Bioxazoline-Derived Ru Metathesis Catalyst. -A new class of ruthenium catalyst based on an IBox-NHC ligand is synthesized. The complex exhibits high stability at elevated temperatures and is a suitable catalyst for olefin metathesis. -(VEHLOW, K.; PORTA, M.; BLECHERT*, S.; ChemCatChem 2 (2010) 7, 803-806,