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20 Aldehyde ketones of type 5 can be synthezised by the reaction of the corresponding salicyl aldehydes, K2CO3 and α-bromo ketones in DMF at r.t.
21 CCDC 607797 (6a) and CCDC 607796 (6f) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
22 All new compounds were fully characterized (IR, NMR, MS, elemental analysis, optical rotation, and melting point).
Enantioselective Intramolecular Crossed-Chromanone Cyclization to 6a; Typical Procedure
In a Schlenk tube under argon at r.t. the pre-catalyst 1 (39.0 mg, 0.104 mmol, 20 mol%) was suspended in anhyd THF (9.5 mL). KHMDS (0.5 M in toluene; 198 µL, 0.099 mmol, 19 mol%) was added slowly, and the solution stirred for 15 min. The yellow solution was cooled to 5 °C and the aldehyde ketone 5a (100 mg, 0.520 mmol) dissolved in anhyd THF (1.0 mL) was added to the carbene solution. The reaction mixture was stirred for 48 h, diluted with CH2Cl2, quenched with H2O, extracted twice with CH2Cl2, and dried over MgSO4. The solvent was evaporated and the crude product was purified by flash chromatography on silica gel (Et2O-n-pentane, 1:8) to yield 6a (88 mg, 88%) as a colorless solid; mp 48 °C; ee 94% [determined by chiral stationary phase GC (Lipodex E)]; [α]D
23 -10.3 (c 1.2, CHCl3). IR (KBr): 3853, 3742, 3482, 2973, 2361, 2340, 1837, 1690, 1610, 1558, 1465, 1382, 1311, 1215, 1134, 1021, 942, 862, 758, 670, 533. 1H NMR (300 MHz, CDCl3, TMS): δ = 0.95 (t, 3 H, J = 7.4 Hz, CH3), 1.81 (q, 2 H, J = 7.5 Hz, CH3CH2), 3.68 (s, 1 H, OH), 4.17 (d, 1 H, J = 11.4 Hz, CHH), 4.40 (d, 1 H, J = 11.4 Hz, CHH), 6.96-7.08 (m, 2 H, Ar), 7.48-7.54 (m, 1 H, Ar), 7.86-7.89 (m, 1 H, Ar). 13C NMR (75 MHz, CDCl3): δ = 6.8 (CH3), 27.6, 72.8 (CH2), 73.0 (C), 117.9 (CH), 118.4 (C), 127.5, 136.5 (CH), 161.4 (C), 196.8 (CO). MS (EI): m/z (%) = 192 (M+, 11), 122 (7), 121 [(M+ + 1) - 72, 100], 120 (11), 93 (7), 92 (18), 77 (5), 65 (6). Anal. Calcd for C11H12O3: C, 68.75; H, 6.29. Found: C, 68.69; H, 6.28.
