Synthesis of 1,4-Diazacycles by Hydrogen Borrowing

We report the syntheses of 1,4-diazacycles by diol-diamine coupling, uniquely made possible with a (pyridyl)phosphine-ligated ruthenium(II) catalyst (1). The reactions can exploit either two sequential N-alkylations or an intermediate tautomerization pathway to yield piperazines and diazepanes; diazepanes are generally inaccessible by catalytic routes. Our conditions tolerate different amines and alcohols that are relevant to key medicinal platforms. We show the syntheses of the drugs cyclizine and homochlorcyclizine in 91% and 67% yields, respectively.

Iridium-Catalyzed Regio- and Diastereoselective Synthesis of C-Substituted Piperazines

Piperazine rings are essential motifs frequently found in commercial drugs. However, synthetic methodologies are mainly limited to N-substituted piperazines, preventing structural diversity. Disclosed herein is a straightforward catalytic method for the synthesis of complex C-substituted piperazines based on an uncommon head-to-head coupling of easily prepared imines. This 100% atom-economic process allows the selective formation of a sole diastereoisomer, a broad substrate scope, and a good functional group tolerance employing a bench-stable iridium catalyst under mild reaction conditions. Key to the success is the addition of N-oxides to the reaction mixture, as they notably enhance the catalytic activity and selectivity.

A Concise Synthetic Method for Constructing 3-Substituted Piperazine-2-Acetic Acid Esters from 1,2-Diamines

We report a short synthetic route for synthesizing 2,3-substituted piperazine acetic acid esters. Optically pure amino acids were efficiently converted into 1,2-diamines that could be utilized to deliver the title 2,3-substituted piperazines in five steps with a high enantiomeric purity. The novel route facilitated, for the first time, the synthesis of 3-phenyl substituted-2-piperazine acetic acid esters that were difficult to achieve using other methods; however, in this case, the products underwent racemization.

One-Pot Synthesis of Enantiopure Pyrrolopiperazines

A simple one-pot protocol for the synthesis of fused pyrrolopiperazines with a complete diastereoselectivity has been developed. This novel methodology combined the Ugi reaction with a spontaneous enamine alkylation on a multicomponent domino reaction, starting from nonprotected diamines and arylglyoxals.

Palladium-Catalyzed Modular Synthesis of Substituted Piperazines and Related Nitrogen Heterocycles

We report here a novel method for the modular synthesis of highly substituted piperazines and related bis-nitrogen heterocycles via a palladium-catalyzed cyclization reaction. The process couples two of the carbons of a propargyl unit with various diamine components to provide nitrogen heterocycles in generally good to excellent yields and high regio- and stereochemical control.

DFT study on the iridium-catalyzed multi-alkylation of alcohol with ammonia

The catalytic mechanism for the multi-alkylation of benzyl alcohols with ammonia catalyzed by the water-soluble catalyst, [Cp*Ir^III(NH₃)₃][I]₂, is computationally investigated by density functional theory (DFT).

Enantioselective synthesis of α-secondary and α-tertiary piperazin-2-ones and piperazines by catalytic asymmetric allylic alkylation

The asymmetric palladium-catalyzed decarboxylative allylic alkylation of differentially N-protected piperazin-2-ones allows the synthesis of a variety of highly enantioenriched tertiary piperazine-2-ones. Deprotection and reduction affords the corresponding tertiary piperazines, which can be employed for the synthesis of medicinally important analogues. The introduction of these chiral tertiary piperazines resulted in imatinib analogues which exhibited comparable antiproliferative activity to that of their corresponding imatinib counterparts.

Substitution of alcohols by N-nucleophiles via transition metal-catalyzed dehydrogenation

This review summarizes the recent advances in transition metal-catalyzed dehydrogenative substitution of alcohols by N-nucleophiles since 2009.

Synthesis of N-aryl substituted, five- and six-membered azacycles using aluminum-amide complexes

N-Aryl substituted, five- and six-membered azacycles, isoindoles and tetrahydroisoquinolines, were synthesized from the reaction of corresponding cyclic ethers (n = 1, 2) with dimethylaluminum-amide reagents.

Pt-Sn/γ-Al2O3-catalyzed highly efficient direct synthesis of secondary and tertiary amines and imines

Versatile syntheses of secondary and tertiary amines by highly efficient direct N-alkylation of primary and secondary amines with alcohols or by deaminative self-coupling of primary amines have been successfully realized by means of a heterogeneous bimetallic Pt-Sn/γ-Al(2)O(3) catalyst (0.5 wt % Pt, Pt/Sn molar ratio=1:3) through a borrowing-hydrogen strategy. In the presence of oxygen, imines were also efficiently prepared from the tandem reactions of amines with alcohols or between two primary amines. The proposed mechanism reveals that an alcohol or amine substrate is initially dehydrogenated to an aldehyde/ketone or NH-imine with concomitant formation of a [PtSn] hydride. Condensation of the aldehyde/ketone species or deamination of the NH-imine intermediate with another molecule of amine forms an N-substituted imine which is then reduced to a new amine product by the in-situ generated [PtSn] hydride under a nitrogen atmosphere or remains unchanged as the final product under an oxygen atmosphere. The Pt-Sn/γ-Al(2)O(3) catalyst can be easily recycled without Pt metal leaching and has exhibited very high catalytic activity toward a wide range of amine and alcohol substrates, which suggests potential for application in the direct production of secondary and tertiary amines and N-substituted imines.