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ÿþPYRIDINIUM CHLORIDE 1 OMe OH Pyridinium Chloride (1), " (3) 83% N " HCl OH OMe OH CO2H CF3 (1), " CF3 HBr, HOAc [628-13-7] C5H6ClN (MW 115.57) (4) or 6N KOH 75% InChI = 1/C5H5N.ClH/c1-2-4-6-5-3-1;/h1-5H;1H InChIKey = AOJFQRQNPXYVLM-UHFFFAOYAN NO2 NO2 NO2 (cleavage of oxiranes to chlorohydrins;3 cleavage of phenol methyl ethers;1,5 removal of N-trityl protecting groups;6 catalyst Cleavage of N-±- and N-Ä-Trityl Groups from Histidine. for Fischer indole synthesis7) The title reagent (1) catalyzes cleavage of trityl protecting groups Alternate Name: pyridine hydrochloride. from the N-± position of histidine, as well as the N-Ä position on æ% Physical Data: mp 144 C (dec). the imidazole moiety of histidine.6 In a typical reaction, the trityl æ% Solubility: sol water, chloroform, ethanol; insol ethyl ether. group is cleaved with 5% of (1) in MeOH at 60 C. It appears to Form Supplied in: white hygroscopic crystalline solid. have application in orthogonal peptide protection schemes. Boc Preparative Method: precipitates as a 98% yield of 99.8% pure and Fmoc protecting groups are unaffected under these conditions white crystals when Hydrogen Chloride gas is passed through (eq 5). a solution of Pyridine in ether.1,2 Purification: recrystallize from chloroform/ethyl acetate and (1), MeOH wash with ethyl ether. Can be dried by refluxing in benzene Trt His(Trt) Lys(Boc) CO2Me " with azeotropic removal of water. Handling, Storage, and Precautions: stable solid, with no appar- H2N His Lys(Boc) CO2Me (5) ent decomposition after several years of storage at room tem- perature. The salt is very hygroscopic and must be protected from moist air. Catalysis of the Fischer Indole Synthesis. Reagent (1) dis- plays utility as a mild catalyst for the Fischer indole synthesis of substrates with strong acid sensitivity (eq 6).7 Cleavage of Oxiranes. The title reagent (1) reacts with a vari- (1), py ety of cyclic and acyclic oxiranes to give chlorohydrins. Typically, PhNHNH2 + O N " a 2:1 ratio of (1) to oxirane is employed and the reactions are car- CO2Et 80% ried out at ambient temperature in chloroform or pyridine (eqs 1 and 2).3 CO2Et N (6) Cl O (1), CHCl3 N (1) OH H Ph Ph rt, 4 h 87% OH (1), CHCl3 1. Prey, V., Chem. Ber. 1942, 75, 445. (2) O rt, 1 h 2. Taylor, M. D.; Grant, L. R., J. Chem. Educ. 1955, 32, 39. Cl 75% 3. Loreto, M. A.; Pellacani, L.; Tardella, P. A., Synth. Commun. 1981, 11, 287. 4. Prey, V., Chem. Ber. 1941, 74, 1219. Cleavage of Phenol Methyl Ethers. Treatment of anisole with æ% 5. Filler, R.; Khan, B. T.; McMullen, C. W., J. Org. Chem. 1962, 27, 4660. 3 equiv of (1) at 200 220 C provides phenol (eq 3).4 A modifica- 6. Sieber, P.; Riniker, B., Tetrahedron Lett. 1987, 28, 6031. tion of the procedure is reported which allows for a more conve- 7. Welch, W. M., Synthesis 1977, 645. nient in situ preparation of (1)5 The use of the title reagent to cleave phenol methyl ethers avoids the strong acidic or basic conditions Michael W. Wilson of alternative methods. This has found utility in the cleavage of Parke-Davis Pharmaceutical Research, Ann Arbor, MI, USA substrates with acid- or base-sensitive moieties (eq 4).5 Avoid Skin Contact with All Reagents

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