Synthesis of Chiral Bisoxazoline Ligands: (3aR,3a'R,8aS,8a'S)-2,2'-(cyclopropane-1,1-diyl)bis(3a,8a-dihydro-8H-indeno[1,2-d]oxazole)

Abstract

A. Bis((3aR,8aS)-3a,8a-dihydro-8H-indeno[1,2-d]oxazol-2-yl)methane (3) . An oven-dried 2-L three-necked, round-bottomed flask equipped with a 6.5 cm × 2.0 cm Teflon-coated elliptical stir bar is fitted with a thermometer, a reflux condenser and a rubber septum. The system is connected to a continuous nitrogen flow and then charged with (1R,2S)-(+)-cis-1-amino-2-indanol (1, 22.2 g, 149 mmol, 2.1 equiv), diethyl malonimidate dihydrochloride (2, 16.4 g, 71 mmol, 1 equiv), and 1 L of dichloromethane (Note 2). The system is heated to 45 °C (internal temperature 43 °C) under an atmosphere of nitrogen in an oil bath for 18 h, stirring at 600 rpm. Reaction progress is monitored by ¹H NMR (Note 3) (Figure 1).

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