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The mixture was stirred overnight at 25 \u00b0C. The pale rose-colored mixture with a fine suspension was cooled at 0 \u00b0C and then allowed to react with solid ammonium chloride (4.4 g, 82.5 mmol) for 4 h at room temperature. The solid was removed by filtration using a Schlenk filter under nitrogen flow and vacuum (15 mmHg). The filtrate was concentrated using a vacuum pump and heated at 40 \u00b0C, affording the crude product (3.9 g, 99% yield). A short path distillation at reduced pressure furnished the pureB-butyl-1,3,2-oxazaborolidine4bas a clear oil (2.0 g, 56%, 98% purity by GC\/MS):\u2009 bp 82 \u00b0C\/0.1 mmHg. IR (\u03bd cm-1):\u2009 3219 (NH). NMR in CDCl3(500 MHz, ppm):\u200911\u0392 \u03b4 35;1H \u03b4 7.3 (m, 5H), 7.50 (d,J= 6 Hz, 1H), 3.9 (m, 1H), 3.5 (br s, 1H, NH), 1.5 (m, 4H), 0.9 (m, 5H), 0.6 (d,J= 6 Hz, 3H);13C \u03b4 139.6, 127.7, 127.2, 126.7, 126.1, 82.1, 53.8, 27.3, 25.4, 20.4, 13.8, 11.3 (br). 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