A Divergent and Selective Synthesis of Isomeric Benzoxazoles from a Single N–Cl Imine

Abstract

A divergent and regioselective synthesis of either 3-substituted benzisoxazoles or 2-substituted benzoxazoles from readily accessible ortho-hydroxyaryl N-H ketimines is described. The reaction proceeds in two distinct pathways through a common N-Cl imine intermediate: (a) N-O bond formation to form benzisoxazole under anhydrous conditions and (b) NaOCl mediated Beckmann-type rearrangement to form benzoxazole, respectively. The reaction path also depends on the electronic nature of the aromatic ring, with the electron-rich aromatic rings favoring the rearrangement and the electron-deficient rings favoring the N-O bond formation. A Beckmann-type rearrangement mechanism via net [1,2]-aryl migration for the formation of 2-substituted benzoxazole is proposed.

Enantioselective Crossed Photocycloadditions of Styrenic Olefins by Lewis Acid Catalyzed Triplet Sensitization

“…Upon irradiation of 4 and styrene with a2 3W CFL, the cycloadduct 12 was isolated in excellent yield, and the major diastereomer was formed with very high enantioselectivity. [13] Styrenes bearing substituents at all positions of the aromatic ring react smoothly and with high ee values (13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23). Av ariety of electron-withdrawing moieties on the styrene ring are readily tolerated.…”

“…Av ariety of electron-withdrawing moieties on the styrene ring are readily tolerated. These include an ester group (16)w hose Lewis basicity did not interfere with the action of the chiral Sc Lewis acid, and potentially UV-sensitive halide substituents (13,14,20,22) which survived irradiation without homolytic degradation. A boronate ester moiety was also readily tolerated (17), providing av ersatile handle for subsequent derivatization of the cycloadduct.…”

Synthesis ofo-(Dimethylamino)aryl Ketones, Acridones, Acridinium Salts, and 1H-Indazoles by the Reaction of Hydrazones and Arynes

“…57 In that process, o -hydroxyaryl ketimines 133 are intramolecularly cyclized to benzisoxazoles 134 or benzoxazoles 135 upon exposure to chlorinating conditions involving respectively a) NCS in the presence of K 2 CO 3 or b) 10% NaOCl.…”

I−/TBHP catalyzed Csp3–N/Csp2–N bond formation via oxidative coupling with benzophenone imine in water

“…[4n] In view of the water-solubility of the most widely used iodine catalyst system (I -/peroxide) [6a] , I -/peroxide system is potential for developing a noble "green" C-N bond formation method. [8] Next, we focused on the choice of substrate. Inspired by the previously reported copper-catalyzed oxidative alkynylation of diaryl imines with terminal alkynes, [7] we chose benzophenone imine 2 as amination reagent in our work not only for its potential oxidative coupling reactivity, but also for its capability of generating primary amine after hydroxylation under acidic condition [ Fig.1, Equation (4)].…”