title: The chlorinating behaviour of WCl₆ towards α-aminoacids.
abstract: Cl/O interchange took place when WCl6 was allowed to interact with a series of α-aminoacids. The α-ammonium-acylchloride salts [NH2(CH2)3CHC(O)Cl][WOCl5], 1a, and [MeNH2CH2C(O)Cl][WOCl5], 1b, were afforded in ca. 55% yields from the reactions of WCl6 with, respectively, L-proline and sarcosine in CH2Cl2. By using other reaction media (hexane or CHCl3), the α-amino-acylchloride complexes WOCl4[O=C(Cl)CH(CH2)3NH2], 5a, and WOCl4[O=C(Cl)CH(R)NHR'] (R = H, R' = Me, 5b; R = R' = H, 5c; R = Me, R' = H, 5d) were isolated in moderate to good yields from WCl6 and, respectively, L-proline, sarcosine, glycine and L-alanine. The formation of 5a,b is basically the result of HCl release from the parent compounds 1a,b. 5a represents a key intermediate in the course of the reaction leading to (WOCl4)2[μ:κ(2)(O)-dkp], 2, dkp = (S,S)-octahydrodipyrrolo[1,2-a:1',2'-d]pyrazine-5,10-dione. 2 was optimally prepared from WCl6/L-proline under high temperature conditions. Hydrolytic treatment of 2 afforded the L-proline-derived 2,5-diketopiperazine (dkp), which was finally isolated with an overall yield of 70%. 1a,b were characterized by X-ray diffractometry, thus providing very rare examples of crystallographically characterized acylchloride derivatives of α-aminoacids. DFT calculations were extensively carried out in order to shed light on structural and mechanistic features.
authors: University of Venezia Ca' Foscari, Dipartimento di Scienze Molecolari e Nanosistemi, Dorsoduro 2137, I-30123 Venezia, Italy.
authors: Marco
authors: M
authors: Bortoluzzi
authors: Fabio
authors: F
authors: Marchetti
authors: Maria Grazia
authors: MG
authors: Murrali
authors: Guido
authors: G
authors: Pampaloni
authors: Stefano
authors: S
authors: Zacchini
mesh_terms: D000596:Amino Acids / Q000737:chemistry*; D002713:Chlorine / Q000737:chemistry*; D018360:Crystallography, X-Ray; D054879:Halogenation; D006860:Hydrogen Bonding; D008958:Models, Molecular; D014414:Tungsten / Q000737:chemistry*
chemical_list: D000596:Amino Acids; D002713:Chlorine; D014414:Tungsten