Dimethylzinc-Mediated, Enantioselective Synthesis of Propargylic Amines

Merging Cobalt-Catalyzed C-H Activation with the Mannich Reaction: A Modular Approach to α-Substituted N-Sulfonyl Amines

A three-component synthesis of α-substituted N-sulfonyl amines from aryl aldehydes, primary sulfonamides, and (hetero)arenes is described. This transformation enables a straightforward and modular synthesis of highly substituted sulfonamide scaffolds in good yields. The direct functionalization of C(sp2)-H bonds via cobalt-catalyzed C-H-activation offers an appealing and atom-economical alternative to classical methods for the synthesis of α-arylated amines such as the Petasis or Mannich-type reactions.

Direct Enantioselective Addition of Alkynes to Imines by a Highly Efficient Palladacycle Catalyst

Enantiopure propargylic amines are highly valuable synthetic building blocks. Much effort has been devoted to develop methods for their preparation. The arguably most important strategy is the 1,2-addition of alkynes to imines. Despite remarkable progress, the known methods using Zn and Cu catalysts suffer from the need for high catalyst loadings, typically ranging from 2-60 mol % for neutral aldimine substrates. Here we report a planar chiral Pd complex acting as very efficient catalyst for direct asymmetric alkyne additions to imines, requiring very low catalyst loadings. Turnover numbers of up to 8700 were accomplished. Our investigation suggests that a Pd-acetylide complex is generated as a catalytically relevant intermediate by the aid of an acac ligand acting as internal catalytic base. It is shown that the catalyst is quite stable under the reaction conditions and that product inhibition is not an issue. A total of 39 examples is shown which all yielded almost enantiopure products.

Development of and recent advances in asymmetric A3 coupling

Asymmetric A3 coupling has emerged as an important class of reactions to synthesise chiral propargylamines. In this tutorial review, an up to date progress of this reaction, with significant recent advancements in terms of ligand development, is presented. Applications of asymmetric A3 coupling in natural product synthesis and in tandem processes are also discussed.

Zn-Catalyzed Multicomponent KA2 Coupling: One-Pot Assembly of Propargylamines Bearing Tetrasubstituted Carbon Centers

Tetrasubstituted propargylamines comprise a unique class of highly useful compounds, which can be accessed through the multicomponent coupling between ketones, amines, and alkynes (KA² coupling), an underexplored transformation. Herein, the development of a novel, highly efficient, and user-friendly catalytic system for the KA² coupling, based on the environmentally benign, inexpensive, and readily available zinc acetate, is described. This system is employed in the multicomponent assembly of unprecedented, tetrasubstituted propargylamines derived from structurally diverse, challenging, and even biorelevant substrates. Notable features of this protocol include the demonstration of the enhancing effect that neat conditions can have on catalytic activity, as well as the expedient functionalization of hindered, prochiral cyclohexanones, linear ketones, and interesting molecular scaffolds such as norcamphor and nornicotine.

Copper/guanidine-catalyzed asymmetric alkynylation of isatin-derived ketimines

Asymmetric alkynylation of isatin-derived ketimines was achieved using an easily available chiral guanidine ligand in combination with CuI under mild reaction conditions.

Mechanistic Studies and Expansion of the Substrate Scope of Direct Enantioselective Alkynylation of α-Ketiminoesters Catalyzed by Adaptable (Phebox)Rhodium(III) Complexes

Mechanistic studies and expansion of the substrate scope of direct enantioselective alkynylation of α-ketiminoesters catalyzed by adaptable (phebox)rhodium(III) complexes are described. The mechanistic studies revealed that less acidic alkyne rather than more acidic acetic acid acted as a proton source in the catalytic cycle, and the generation of more active (acetato-κ(2)O,O')(alkynyl)(phebox)rhodium(III) complexes from the starting (diacetato)rhodium(III) complexes limited the overall reactivity of the reaction. These findings, as well as facile exchange of the alkynyl ligand on the (alkynyl)rhodium(III) complexes led us to use (acetato-κ(2)O,O')(trimethylsilylethynyl)(phebox)rhodium(III) complexes as a general precatalyst for various (alkynyl)rhodium(III) complexes. Use of the (trimethylsilylethynyl)rhodium(III) complexes as precatalysts enhanced the catalytic performance of the reactions with an α-ketiminoester derived from ethyl trifluoropyruvate at a catalyst loading as low as 0.5 mol % and expanded the substrate scope to unprecedented α-ketiminophosphonate and cyclic N-sulfonyl α-ketiminoesters.

Indium(iii)-catalyzed tandem synthesis of 2-alkynyl-3,3-dichloropyrrolidines and their conversion to 3-chloropyrroles

A convenient route to 2-alkynyl-3,3-dichloropyrrolidines was described by addition of terminal acetylenes to 2,2,4-trichloroaldimines using In(OTf)₃ as a catalyst. In the presence of a base these pyrrolidines were transformed into 3-chloropyrroles.

Palladium-catalyzed N-nitroso-directed C-H alkoxylation of arenes and subsequent formation of 2-alkoxy-N-alkylarylamines

A palladium-catalyzed direct ortho-alkoxylation of N-alkyl-N-nitrosoarylamines was developed in which alcohols were used as the alkoxylation reagents and PhI(OAc)2 was employed as the oxidant. The protocol was available for both primary and secondary alcohols. The products were transformed to o-alkoxy-N-alkylanilines expediently by a simple reduction.

A single Cu(II) catalyst for the three-component coupling of diverse nitrogen sources with aldehydes and alkynes

A single Cu(II) catalyst without the addition of ligand or base couples a diverse range of nitrogen sources with alkynes and aldehydes bearing alkyl, halogenated, silyl, aryl, and heteroaryl groups. The first example of a copper-catalyzed alkynylation involving p-toluenesulfonamide provides high yields of N-Ts-protected propargylamines. The superior activity of copper(II) triflate also allows this three-component alkynylation to incorporate a ketone.

Highly enantioselective zinc/BINOL-catalyzed alkynylation of α-ketoimine ester: a new entry to optically active quaternary α-CF3 α-amino acids

An effective method for highly enantioselective alkynylation of ketoimine (α-trifluoromethyl ketoimine ester) has been developed via a zinc/BINOL catalyzed process. This protocol provides a useful and facile access to optically active quaternary α-trifluoromethyl α-amino acids and related derivatives of interest in life sciences.

Synthesis of copper(I) complexes containing enantiopure pybox ligands. First assays on enantioselective synthesis of propargylamines catalyzed by isolated copper(I) complexes

Dinuclear [Cu(2)(R-pybox)(2)][X](2) [X = PF(6), R-pybox = 2,6-bis[4'-(S)-isopropyloxazolin-2'-yl]pyridine (S,S)-(i)Pr-pybox (1), 2,6-bis[4'-(R)-phenyloxazolin-2'-yl]pyridine) (R,R)-Ph-pybox (2), 2,6-bis[4'-(S)-isopropyl-5',5'-difeniloxazolin-2'-yl]pyridine (S,S)-(i)Pr-pybox-diPh (3); X = OTf, (R,R)-Ph-pybox (4)] and mononuclear complexes [Cu(R-pybox)(2)][PF(6)] [R-pybox = (S,S)-(i)Pr-pybox (5), (R,R)-Ph-pybox (6)] have been diastereoselectively prepared by reaction of [Cu(MeCN)(4)][PF(6)] or CuOTf.0.5C(6)H(6) and the corresponding pybox ligand. The reaction of CuX (X = I, Br, Cl) with substituted pybox in a 2:1 molar ratio allows us to synthesize tetranuclear complexes [Cu(4)X(4)(R-pybox}(2)] [R-pybox = (S,S)-(i)Pr-pybox, X = I (7), Br (8); (R,R)-Ph-pybox, X = I (9), Br (10), Cl (11); (S,S)-(i)Pr-pybox-diPh, X = I (12), Cl (13)]. Dinuclear complexes [Cu(2)(mu-Cl)(R-pybox)(2)][CuCl(2)] [R-pybox = (S,S)-(i)Pr-pybox (15), (R,R)-Ph-pybox (16)] have been prepared by reaction of CuCl with (i)Pr-pybox or Ph-pybox in 3:2 molar ratio. The structures of the complexes 1, 2, 7, 15, 16 and that of the polymeric species [Cu(4)(mu(3)-Br)(3)(mu-Br)((i)Pr-pybox)](n) (14) have been determined by single-crystal X-ray diffraction analysis. Diffusion studies using (1)H and (19)F-DOSY experiments provide evidence that the different nuclearity of compounds 1 and 5 is maintained in the solution state and confirm that these ionic compounds exist in solution as stable, discrete, cationic complexes. The complexes 1-4, 6, 9, 10, and 16 as well as the previously reported [Cu(2){(S,S)-(i)Pr-pybox}(2)][OTf](2) have been assayed as catalysts in the enantioselective synthesis of propargylamines. The dinuclear complexes [Cu(2){(R,R)-Ph-pybox}(2)][X](2) (2, 4) were found to be the most efficient catalysts (up to 89% e.e.).