The solid-phase synthesis and use of N-monosubstituted piperazines in chemical library synthesis

Ring-opening metathesis polymerization-based recyclable magnetic acylation reagents

An operationally simple method for the acylation of amines utilizing carbon-coated metal nanoparticles as recyclable supports is reported. Highly magnetic carbon-coated cobalt (Co/C) and iron (Fe/C) nanobeads were functionalized with a norbornene tag (Nb-tag) through a "click" reaction followed by surface activation employing Grubbs-II catalyst and subsequent grafting of acylated N-hydroxysuccinimide ROMPgels (ROMP=ring-opening metathesis polymerization). The high loading (up to 2.6 mmolg(-1) ) hybrid material was applied in the acylation of various primary and secondary amines. The products were isolated in high yields (86-99%) and excellent purities (all >95 % by NMR spectroscopy) after rapid magnetic decantation and simple evaporation of the solvents. The spent resins were successfully re-acylated by acid chlorides, anhydrides, and carboxylic acids and reused for up to five consecutive cycles without considerable loss of activity.

One-step cyclization: synthesis of N-heteroalkyl-N'-tosylpiperazines

Piperazine derivatives are important intermediates in organic synthesis and useful building blocks in pharmaceutical and fine chemical industries. Currently available synthetic routes for these heterocyclic compounds have limited scope owing to the harsh reaction conditions, low yields, and multistep process. Herein, we reported a practical method for synthesis of alkyl-, alcohol-, amine-, and ester-extended tosylpiperazines under mild conditions with moderate to high yields. This protocol exhibits potential applicability in the synthesis of pharmaceuticals and natural products because of the operational simplicity and the conveniently available reactants. On the basis of the experimental and theoretical results, a plausible mechanism of aliphatic nucleophilic substitution (S(N)) in the cyclization has been postulated and evidence for the formation of a six-membered ring has also been confirmed by means of density functional theory (DFT) calculations.

Annulation of Primary Amines to Piperazines and Diazaspirocycles Utilizing α-Methyl Benzyl Resin

The microwave-assisted solid-phase synthesis of piperazines, 3,9-diazaspiro[5.5]undecanes and 2,9-diazaspiro[5.5]undecanes is reported. The synthesis relies on the direct annulation of primary amines with resin-bound bismesylates. Critical to the success of this chemistry was the development of alpha-methyl benzyl carbamate resin linker. This resin permits the cleavage of the heterocycles under mildly acidic conditions, free of contaminating linker-derived N-alkylated byproducts.

Solid-Phase Polyamine Synthesis Using Piperazine and Piperidine Building Blocks

[reaction: see text]. Polyamines containing piperidine and piperazine moieties have been synthesized on solid support using SN2 alkylation of resin-bound secondary amines with 2-nitrobenzenesulfonates (nosylates). The effect of solvent on this alkylation was investigated. The methodology was employed for the total synthesis of novel analogues of wasp polyamine toxins (philanthotoxins).