Stereospecific Single-Pot Route to Chiral Imidazolidines from Aziridines Using a 2D Cu Metal–Organic Framework

Abstract

The role of coordinatively unsaturated sites (CUS) in metal−organic framework (MOF)-catalyzed organic transformation is vital; however, the design and generation of such sites are challenging. We, therefore, report the synthesis of a novel two-dimensional (2D) MOF, [Cu(BTC)(Mim)] n (Cu-SKU-3), with pre-existing unsaturated Lewis acid sites. The presence of these active CUS facilitates a ready-to-use attribute in Cu-SKU-3, thereby subsiding the lengthy activation processes associated with MOF-based catalysis. The material has been completely characterized using single crystal X-ray diffraction (SCXRD), powder XRD (PXRD), thermogravimetric analysis (TGA), carbon, hydrogen, and nitrogen (CHN), Fourier-transform infrared (FTIR), and Brunauer−Emmett−Teller (BET) surface area analyses. We directly utilize Cu-SKU-3 for the synthesis of biologically valued chiral imidazolidine motifs in a one-pot fashion starting from aziridines. The chiral imidazolidines are synthesized in good yield (up to 89%) and with high optical purity (ee > 98−99%). Mechanistically, the transformation proceeds in a tandem fashion through stereospecific ring-opening of aziridines followed by the intramolecular cyclization (via sp 3 C−H functionalization) reaction forming chiral imidazolidines. The material has an excellent heterogeneous attribute and can be reused several times for one-pot catalytic cycles.

B2(OH)4-Mediated Reductive Ring-Opening of N-Tosyl Aziridines by Nitroarenes: A Green and Regioselective Access to Vicinal Diamines

“…For example, in the earliest report by Yamamoto and co-workers, who used Yb­(OTf) 3 to catalyze the aziridine ring-opening by amines, the regioselectivity for aryl amines was only low to moderate and 10 equiv of amines is required. Afterward, a wide range of metal Lewis acids, B­(C 6 F 5 ) 3 , phosphines, amines, metal–organic frameworks (MOFs), and aminium radical-cation salts have been introduced as catalysts for the aminolysis of aziridines (Scheme b). More recently, the catalyst and solvent-free ring-openings of aziridines were also developed …”

Construction of C–X (X = N, O) bonds from benzyl alcohols via Cu-BTC-catalyzed oxidative coupling

“…23 Especially in catalysis, MOFs, as emerging porous non-homogeneous catalysts, show remarkable potential 24 in reactions such as oxidations, 25 reductions, 26 couplings 27 and cyclisations. 28 [Cu 3 (BTC) 2 (H 2 O) 3 ] n (Cu-BTC, HKUST-1), as a typical representative of MOFs, has been widely used in a variety of organic reactions, 29 including couplings, 30 cyclizations, 31 oxidizations 32 and boronation reactions. 33 However, the Cu-BTC-catalyzed construction of C–X bonds is still under investigation.…”