Metal-Assisted Ring-Closing/Opening Process of a Chiral Tetrahydroquinazoline

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• 作者：Ana M. Garc铆a-Deibe ; Jes煤s Sanmart铆n-Matalobos ; Concepci贸n Gonz谩lez-Bello ; Emilio Lence ; Cristina Portela-Garc铆a ; Luis Mart铆nez-Rodr铆guez ; Matilde Fondo
• 刊名：Inorganic Chemistry
• 出版年：2012
• 出版时间：February 6, 2012
• 年：2012
• 卷：51
• 期：3
• 页码：1278-1293
• 全文大小：819K
• 年卷期：v.51,no.3(February 6, 2012)
• ISSN：1520-510X

文摘

The ring鈥揷hain tautomerism of a 2-aryl-1,2,3,4-tetrahydroquinazoline has been exploited to induce reversible changes in the aminal鈥搃mine equilibrium, as desired, by coordination of a suitable metal ion. This process was studied by NMR and UV鈥搗is spectroscopies, X-ray crystallography, and molecular modeling approach. The results obtained show that the imine H₂Lⁱ undergoes a selective ring-closing reaction upon complexation with Ni²⁺. As a result, complexes of the type Ni(HL^a)₂ are obtained, whose chirality arises from the chiral ligand H₂L^a and the helicity of the structure. Hence, helical enantiomers form the following racemates: [螖-C(R,R)N(S,S),螞-C(S,S)N(R,R)]-Ni(HL^a)₂路2HOAc and [螖,螞-C(S,R)N(R,S)]-Ni(HL^a)₂路4MeOH. In contrast to the situation observed for Ni²⁺, the cyclic tautomer of the ligand, H₂L^a, undergoes a selective ring-opening reaction upon complex formation with Pd²⁺, ultimately yielding Pd(HLⁱ)₂路MeOH, in which the open-chain imine ligand is bidentate through the N,O donor set of the quinoline residue. Density functional theory calculations were conducted to provide insight into the different behavior of both coordinated metals (Ni²⁺ and Pd²⁺) and to propose a mechanism for the metal-assisted opening/closing reaction of the tetrahydroquinazoline ring.