Catalytic Enantioselective Halocyclizations to Access Benzoxazepinones and Benzoxazecinones

Catalytic Enantioselective Chlorofunctionalizations of N-Substituted Amides Using In Situ Generated HOCl as Hydrogen Bond Source

Asymmetric organocatalytic halocyclization represents a powerful method for the synthesis of valuable chiral haloheterocycles. However, its heavy dependence on substrates that contain hydrogen bond donors for enantiocontrol limits its broader application. Here we report a catalytic asymmetric chlorofunctionalization of olefinic amides that do not bear hydrogen bond donors, allowing for the efficient production of chlorooxazolidin-2-ones and chloroamino esters featuring quaternary stereocenters, achieved with high yields and excellent enantioselectivity. This catalytic protocol facilitates the synthesis of N-aryloxazolidin-2-ones and establishes a useful framework for synthesizing antibiotic analogues. Mechanistic studies indicate that trace amounts of water interact with the chlorinating agent to produce HOCl in situ, which acts as both a proton donor and a hypochlorite source, thereby promoting the asymmetric cyclization process. This strategy significantly broadens the potential of halocyclization for the development of a diverse array of functional molecules.

Visible-Light-Catalyzed Fast Synthesis of 1,4-Benzoxazepine Derivatives from 2-Alkoxyarylaldehydes and N-Arylglycines

A novel photocatalytic method for the synthesis of 1,4-benzoxazepine using 2-alkoxyarylaldehyde as an oxygen source and N-arylglycine as a nitrogen source has been reported. This method is mild, efficient, and fast, and the corresponding reaction can be completed within 2 h at room temperature under a nitrogen atmosphere and light-irradiation conditions. Mechanistic studies have confirmed that this scheme involves the decarboxylation cyclization of N-arylglycine and provides a convenient pathway for the preparation of various 2-alkyl-N-phenyl-substituted 1,4-benzoxazepine.

Synthesis of 1,4-benzodioxepines via electrochemical oxyselenenylation of 2-O-tethered alkenyl phenylmethanol and diselenides

A highly efficient methodology has been developed for the synthesis of 1,4-benzodioxepines through electrochemical oxyselenenylation of 2-O-tethered alkenyl phenylmethanol and diselenides under external oxidant-free conditions at room temperature. Experimental evidence supports this transformation to occur via a radical mechanism.

Organocatalytic Enantioselective Chloroiminocyclization for the Synthesis of Imidazoline

Imidazoline is an important scaffold in organic synthesis and a pharmacophore in medicinal chemistry. We apply basic imines as nucleophiles for the catalytic asymmetric chloroiminocyclization to furnish tetrasubstituted stereocenter-containing imidazolines in excellent yields and enantioselectivities. The reaction can be conducted in the polar solvent acetonitrile under concentrated reaction conditions.

Enantiospecific Analysis of Carboxylic Acids Using Cinchona Alkaloid Dimers as Chiral Solvating Agents

Cinchona alkaloid derivatives as Brønsted base catalysts have attracted considerable attention in the field of asymmetric catalysis. However, their potential application as chiral solvating agents has not been described. In this research, we investigated the use of the Cinchona alkaloid dimer, namely, (DHQ)2PHAL, as a chiral solvating agent for discerning various mandelic acid derivatives through 1H NMR spectroscopy. The addition of catalytic amounts of DMAP facilitated this process. Our experimental results demonstrate that dimeric (DHQ)2PHAL exhibits remarkable chiral discrimination properties regarding the diagnostic split protons of 1H NMR signals (including 24 examples, up to 0.321 ppm). Furthermore, it serves as an excellent chiral discriminating agent and provides good resolution for racemic chiral phosphoric acid as determined by 31P NMR spectroscopy. The quality of enantiodifferentiation has also been evaluated by means of the parameter "resolution (Rs)". Significantly, this class of CSAs based on (alkaloid)2linker systems with an azaaromatic linker can be directly employed, which is commercially available in an enantiopure form at very low cost and exhibits promising potential in determining the enantiopurity of α-hydroxy acids by chemoselective and biocatalytic reactions.

Synthesis of Benzodioxepinones and Benzoxazepinones via Tandem Oxidation and Iodolactonization of 2-O/N-tethered Alkenyl Benzaldehyde Mediated by CuI/TBHP

An efficient methodology for the synthesis of halogenated benzodioxepinones and benzoxazecinones has been developed via tandem oxidation and iodolactonization reaction of 2-O/N-tethered alkenyl benzaldehydes mediated by CuI and tertiarybutylhydro-peroxide in acetonitrile at 70 °C in moderate to good yields. The reaction involves initial oxidation of aldehyde to acid followed by iodolactonization. Terminal propargyl ether resulted in a mixture of mono- and diiodido-3-methylene-1,4-dioxepin-5-ones. The post-synthetic modification of the reaction products leads to the formation of corresponding thiocyanate, azide, thioether, and triazole derivatives.

I2/CF3CO2Ag-mediated iodolactonization of various allenoic acids to access versatile 6- to 9-membered ring vinylic iodolactones

Medium-sized lactones are important structural units, but their synthesis remains a great challenge. Herein, we report I2/CF3CO2Ag-mediated iodolactonization of allenoic acids to synthesize various 6- to 9-membered ring vinylic iodolactones in 16-89% yield. This protocol not only develops a new cyclization strategy of allenoic acids, but also provides highly functionalized medium-sized lactones containing alkene and halogen groups.

Organocatalyzed enantio- and diastereoselective isomerization of prochiral 1,3-cyclohexanediones into nonalactones bearing distant stereocenters

The lactonization of 2-(2-nitrophenyl)-1,3-cyclohexanediones containing an alcohol side chain and up to three distant prochiral elements is reported by isomerization under the mediation of simple organocatalysts such as quinidine. Through a process of ring expansion, strained nonalactones and decalactone are produced with up to three stereocenters in high er and dr (up to 99 : 1). Distant groups, including alkyl, aryl, carboxylate and carboxamide moieties, were examined.

Enantioselective iodolactonization to prepare ε-lactone rings using hypervalent iodine

Despite the rapid growth of enantioselective halolactonization reactions in recent years, most are effective only when forming smaller (6,5,4-membered) rings. Seven-membered ε-lactones, are rarely formed with high selectivity, and never without conformational bias. We describe the first highly enantioselective 7-exo-trig iodolactonizations of conformationally unbiased ε-unsaturated carboxylic acids, effected by an unusual combination of a bifunctional BAM catalyst, I₂, and I(iii) reagent (PhI(OAc)₂:PIDA).

We describe the first highly enantioselective 7-exo-trig iodolactonizations of conformationally unbiased ε-unsaturated carboxylic acids, effected by an unusual combination of a bifunctional BAM catalyst, I₂, and I(iii) reagent (PhI(OAc)₂:PIDA).

Accessing Chiral 2,2-Disubstituted Morpholines via Organocatalytic Enantioselective Chlorocycloetherification

Chiral morpholine is an important scaffold in organic synthesis and a pharmacophore in medicinal chemistry. However, catalytic enantioselective procedure for the construction of morpholine remains sparse. We report herein a...