Efficient N-Arylation/Dealkylation of Electron Deficient Heteroaryl Chlorides and Bicyclic Tertiary Amines under Microwave Irradiation

Reactions of Polychlorinated Pyrimidines with DABCO

The reaction of 2,4,5,6-tetrachloropyrimidine (4) and 4,5,6-trichloropyrimidine-2-carbonitrile (1) with DABCO (1 equiv.), in MeCN, at ca. 20 °C gives 2,4,5-trichloro-6-[4-(2-chloroethyl)piperazin-1-yl]pyrimidine (5) and 4,5-dichloro-6-[4-(2-chloroethyl)piperazin-1-yl]pyrimidine-2-carbonitrile (6) in 42% and 52% yields, respectively. The new compounds were fully characterized.

Metal-Free Synthesis of 2- N, N-Dialkylaminobenzoxazoles Using Tertiary Amines as the Nitrogen Source

The unprecedented reaction of tertiary amines with 2(3 H)-benzoxazolones has been investigated. In the presence of the Ph₃P-I₂ reagent system, the reaction of both acyclic and cyclic aliphatic tertiary amines led to the formation of 2- N, N-dialkylaminobenzoxazoles with the selective cleavage of an alkyl group. Especially, N-(2-iodoethyl)piperazinyl derivatives were rapidly produced in good yields when using DABCO as the nitrogen source. Only in the cases when the nucleophilicity of the substrates exceeds that of the amine, competitive self-condensation of benzoxazolones then proceeds preferentially. ³¹P{¹H}-NMR study suggested the involvement of an aryloxyphosphonium intermediate and/or possibly 2-iodobenzoxazole which activates the C-2 position of benzoxazolones toward nucleophilic aromatic substitution.

Sulfonylation of 1,4-Diazabicyclo[2.2.2]octane: Charge-Transfer Complex Triggered C-N Bond Cleavage

A novel charge-transfer complex triggered sulfonylation of 1,4-diazabicyclo[2.2.2]octane (DABCO) with mild reaction conditions has been developed. The formation of a charge-transfer complex between electron-withdrawing (hetero)aryl sulfonyl chloride and DABCO allows the synthesis of N-ethylated piperazine sulfonamide in good yields. The reaction has a high functional group tolerance. Spectroscopic studies confirmed the charge-transfer complex formation between sulfonyl chlorides and DABCO, which facilitates the C-N bond cleavage of DABCO.

DABCO bond cleavage for the synthesis of piperazine derivatives

The applications of DABCO (1,4-diazabicyclo[2.2.2]octane) in the synthesis of piperazine derivatives including biologically active compounds via C–N bond cleavage are investigated in this review. Different reagents such as alkyl halides, aryl(heteroary) halides, carboxylic acids, diaryliodonium salts, tosyl halides, activated alkynes, benzynes etc. were applied for the preparation of the corresponding quaternary ammonium salts of DABCO, which are very good electrophiles for various nucleophiles such as phenols, thiophenols, thiols, alcohols, aliphatic and aromatic amines, sulfinates, phthalimide, indoles, NaN₃, triazole and terazoles, NaCN, enols and enolates, halides, carboxylic acid salts etc. Besides preactivated DABCO salts, the in situ activation of DABCO in multicomponent reactions is also an efficient tactic in synthetic organic chemistry for the diversity oriented synthesis of drug-like piperazine derivatives.

The applications of DABCO (1,4-diazabicyclo[2.2.2]octane) in the synthesis of piperazine derivatives including biologically active compounds via C–N bond cleavage are investigated in this review.

N-Arylation of DABCO with Diaryliodonium Salts: General Synthesis of N-Aryl-DABCO Salts as Precursors for 1,4-Disubstituted Piperazines

Employing DABCO as a substrate, aryl(mesityl)iodonium triflates are introduced as arylating agents for a tertiary sp³-nitrogen. Mild conditions and exceptional selectivity of the aryl group transfer allow unprecedented N-aryl-DABCO salts to be obtained, bearing substituents of different electronic natures. This metal-free methodology has no analogy among known transition-metal-based reactions. The utility of isolated N-aryl-DABCO salts is demonstrated for the preparation of flibanserin.