Piperazine reagent

Ellwood P.A., Hardy H.L. and Walker R.F. (1981) Determination of atmospheric isocyanate concentrations by high-performance thin-layer chromatography using l-(2-pyridyl)-piperazine reagent. Analyst, 106, 85-93. 

Table 10. Removal of fluorenylmethoxycarbonyl (Fmoc) group from relatively hydrophobic substrates and scavenging of the by-product dibenzofulvene (DBF) by different polymeric piperazine reagents...

RO membranes are formed as an ultrathin aromatic polyamide (PA) layer through interfacial polymerization, as shown in Fig. 4.8 (a), on an ultra porous polyether sulfone (PES), made by phase inversion technique [18, 19]. The PES substrate is soaked in 1% aqueous solution of MPD for 1 min. After draining olT excess water, the substrate was immersed in hexane bath containing 0.1% TMC for 30 sec. The membrane is then heated in an oven at 70° C for 5 min to obtain RO membrane of 1 A pore diameter, which corresponds to a MWCO of 50 Da. Similar procedme is followed for preparing NF membrane except that MPD was replaced with piperazine reagent to obtain a pore size of 15-20 A with MWCO 400 Da, as depicted in Fig. 4.8 (b). 

Piperazine linker 77 was treated with propargyltriphenylphosphine bromide to provide a resin-bound Wittig reagent (Scheme 40) [89]. Base treatment followed by aldehyde addition produced a resin-bound 2-amino-butadiene which was implemented in [4 + 2] cycloadditions. Alternatively, treatment with 3% TFA in CH2CI2 released a,(J-unsaturated methylke-tones in high yields. 

Similarly, a solid-supported imide has been reported to serve as an acylating reagent under microwave conditions by Nicewonger and coworkers [130], The starting imide was immobilized on aminomethyl polystyrene and in this case benzoyl chloride was chosen to prepare the acylating reagent (Scheme 7.111). Primary amines and piperazines were smoothly acylated at room temperature, but more hindered secondary amines required more time and higher temperatures, and anilines... 

Kwakman et al. [65] described the synthesis of a new dansyl derivative for carboxylic acids. The label, N- (bromoacetyl)-A -[5-(dimethylamino)naphthalene-l-sulfonyl]-piperazine, reacted with both aliphatic and aromatic carboxylic acids in less than 30 min. Excess reagent was converted to a relatively polar compound and subsequently separated from the derivatives on a silica cartridge. A separation of carboxylic acid enantiomers was performed after labeling with either of three chiral labels and the applicability of the method was demonstrated by determinations of racemic ibuprofen in rat plasma and human urine [66], Other examples of labels used to derivatize carboxylic acids are 3-aminoperylene [67], various coumarin compounds [68], 9-anthracenemethanol [69], 6,7-dimethoxy-l-methyl-2(lH)-quinoxalinone-3-propionylcarboxylic acid hydrazide (quinoxalinone) [70], and a quinolizinocoumarin derivative termed Lumarin 4 [71],... 

Piperazine-2,5-diones react with trimethyloxonium fluoroborate (Meer-wein s reagent) or triethyloxonium fluoroborate to generate the corresponding lactim ethers. 

Piperazine-2,5-diones, in which both amino acid units are primary, lead to bislactim ethers on O-alkylation with Meerwein s reagents. No selectivity in this reaction has been demonstrated so far. Such bislactim ethers (171) have been prepared and extensively used by Schollkopf and his school [79AG(E)863, and later papers]. During the preparation of these bislactim ethers, neutralization of the initially formed bis-tetrafluoroborate salt is carried out with phosphate buffer to avoid racemization. 

Aziridine is converted into piperazine on NH3 treatment 1-substituted aziridines give 1,4-disubstituted piperazines when reacted with Grignard reagents. Azirines (326) with Group VI metal carbonyls give pyrazines (327) and dihydropyrazines (328). 

Keywords acyl chloride, 77-alkyl piperazine, Lawesson s reagent, microwave irradiation, thioamide... 

Representative Sample of the Reagents Used in the 5000-Member 4-Alkyl-piperazine-2-carboxamide Combinatorial Library0... 

An efficient, practical solid-phase synthesis of a variety of bis-hetero-cyclic compounds was developed starting from resin-bound orthogonally protected lysine (Fig. 10). Tetraamines 36 were synthesized by exhaustive reduction of resin-bound tetraamides 35. Cyclization with different commercially available bifunctional reagents such as cyanogen bromide, thio-carbonyldiimidazole, carbonyldiimidazole, and oxalyldiimidazole yielded the corresponding bis-heterocyclic compounds bis-cyclic guanidines 37,39 bis-cyclic thioureas 38, bis-cyclic ureas 39, and bis-diketopiperazines 40, respectively.40 Reduction of compounds 40 led to bis-piperazines 41. 

One approach utilizes Katritzky s route to tertiary amines to construct the benzhydrylpiperazine (Scheme 7) [42]. This method involves addition of an aryl Grignard reagent to a masked iminium, an adduct formed from the piperazine, an appropriate benzaldehyde, and benzotriazole. In solution, this adduct is in equilibrium with an iminium ion formed by elimination of the benzotriazole, and it is likely that the Grignard reagent adds to this species. Assuming that the iminium ion is the reactive entity, the stereoselectivity appears to rely on two separate events 1) preferential formation of one of the... 

Most such processes have involved treatment with an alkyl halide or with an (activated) aryl or heteroaryl halide in the presence of a base but many other reagents have been used as well. Naturally, piperazines can undergo mono- or dialkylation, broadly according to the amount of reagent, but sometimes prior protection of one NH grouping may be necessary to avoid any dialkylation. The following classified examples illustrate recently reported alkylation processes ... 

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