HETEROCYCLES, Vol. 77, No. 2, 2009
1293
ratio) as a colorless crystal.
1H NMR (500 MHz, CDCl3, δ): (major) 3.40 (qd, JHF = 9.1, 3.6 Hz, 1H), 4.07 (ddq, J = 12.4, 3.6, 1.8 Hz,
1H), 4.59 (d, J = 12.4 Hz, 1H), 5.66 (s, 1H), 6.79 (d, J = 7.5 Hz, 1H), 7.21 (dd, J = 7.5, 7.5 Hz, 1H), 7.25
(dd, J = 7.5, 7.5 Hz, 1H), 7.34–7.37 (m, 5H), 7.39 (d, J = 7.5 Hz, 1H); (minor) 3.52–3.57 (m, 1H), 4.05–
4.12 (m, 2H), 5.88 (s, 1H), 6.93 (d, J = 7.4 Hz, 1H), 7.19–7.22 (m, 2H), 7.27–7.38 (m, 5H), 7.47 (d, J =
13
7.4 Hz, 1H). C NMR (126 MHz, CDCl3, δ): (major) 41.5 (q, JCF = 26 Hz), 63.6 (q, JCF = 3 Hz), 80.5,
126.2 (q, JCF = 281 Hz), 126.4 (q, JCF = 2 Hz), 126.9, 127.1, 128.4, 128.5, 128.6, 128.9, 130.2, 138.9,
141.1; (minor) 41.3 (q, JCF = 26 Hz), 59.4 (q, JCF = 3 Hz), 77.8, 126.3 (q, JCF = 281 Hz), 127.2 (q, JCF = 2
19
Hz), 127.2, 127.5, 127.9, 128.3, 128.4, 129.1, 129.6, 137.1, 140.9. F NMR (470 MHz, CDCl3, δF):
(major) 93.9 (d, JFH = 9 Hz); (minor) 93.8 (d, JFH = 9 Hz). IR (neat): 3064, 3031, 2870, 1455, 1355, 1243,
1155, 999, 747, 700 cm-1. Anal. Calcd for C16H13OF3: C, 69.06; H, 4.71. Found: C, 69.08; H, 4.94.
4-Difluoromethylene-3,4-dihydro-1H-2-benzopyran (8a): Compound 8a was prepared by the method
described for 8c (vide infra). Purification by PTLC (pentane–Et2O 5:1) gave 8a (38%) as a colorless
1
liquid. H NMR (500 MHz, CDCl3, δ): 4.50 (dd, JHF = 2.7, 2.7 Hz, 2H), 4.79 (s, 2H), 7.05 (d, J = 7.5 Hz,
13
1H), 7.21 (dd, J = 7.5, 7.5 Hz, 1H), 7.27 (dd, J = 7.5, 7.5 Hz, 1H), 7.61 (d, J = 7.5 Hz, 1H). C NMR
(126 MHz, CDCl3, δ): 63.2 (dd, JCF = 4, 4 Hz), 68.9, 85.7 (dd, JCF = 20, 13 Hz), 124.7, 125.7 (d, JCF = 3
Hz), 126.6 (dd, JCF = 10, 5 Hz), 127.0 (dd, JCF = 2, 2 Hz), 127.3, 134.1 (dd, JCF = 5, 3 Hz), 152.3 (dd, JCF
= 296, 291 Hz). 19F NMR (470 MHz, CDCl3, δF): 75.6 (d, JFF = 41 Hz, 1F), 75.5 (d, JFF = 41 Hz, 1F). IR
(neat): 2958, 2846, 1722, 1329, 1261, 1236, 1086, 1053, 760, 737 cm-1. Anal. Calcd for C10H8OF2: C,
65.93; H, 4.43. Found: C, 66.07; H, 4.59.
4-Difluoromethylene-1-phenyl-3,4-dihydro-1H-2-benzopyran (8c): To a solution of 8c (53 mg, 0.19
mmol) in DMF (2.0 mL) was added K3PO4 (81 mg, 0.38 mmol) at rt. After the reaction mixture was
stirred at 120 °C for 6 h, phosphate buffer (pH 7) was added to quench the reaction. Organic materials
were extracted with Et2O three times. The combined extracts were washed with brine and dried over
Na2SO4. After removal of the solvent under reduced pressure, the residue was purified by PTLC
1
(pentane–Et2O 5:1) to give 8c (21 mg, 43%) as a colorless liquid. H NMR (500 MHz, CDCl3, δ): 4.43
(ddd, J = 13.2 Hz, JHF = 3.6, 3.6 Hz, 1H), 4.63 (dd, J = 13.2 Hz, JHF = 2.6 Hz, 1H), 5.76 (s, 1H), 6.81 (d, J
= 7.6 Hz, 1H), 7.13 (dd, J = 7.6, 7.6 Hz, 1H), 7.24–7.39 (m, 6H), 7.66 (d, J = 7.6 Hz, 1H). 13C NMR (126
MHz, CDCl3, δ): 61.0 (dd, JCF = 4, 4 Hz), 80.0, 86.0 (dd, JCF = 24, 8 Hz), 126.4 (dd, JCF = 4, 2 Hz), 126.5
(dd, JCF = 14, 2 Hz), 126.9 (dd, JCF = 2, 2 Hz), 127.1, 127.5, 128.4, 128.5, 128.8, 136.5 (dd, JCF = 6, 2 Hz),
140.7, 152.2 (dd, JCF = 300, 287 Hz). 19F NMR (470 MHz, CDCl3, δF): 75.5 (d, JFF = 41 Hz, 1F), 75.9 (d,
JFF = 41 Hz, 1F). IR (neat): 3066, 3032, 2927, 2854, 1732, 1718, 1238, 760, 700 cm-1. Anal. Calcd for
C16H12OF2: C, 74.41; H, 4.68. Found: C, 74.42; H, 4.91.
4-Trifluoromethyl-3,4-dihydro-1H-2-benzothiopyran (9a): To a solution of 6a (44 mg, 0.17 mmol) in