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Procedure for the Carboxylation 1 → 2: n-BuLi (1.86 mL, 2.50 M in hexanes, 4.65 mmol) was added at 0 °C to a solution of 1.26 g (3.88 mmol) of 1 in 25 mL of dry cyclohexane. The mixture was stirred at r.t. for 3 h, recooled to 0 °C and 1.00 mL (12.9 mmol) of methyl chloroformate were added. Stirring was continued overnight and the reaction was allowed to warm up to r.t. After quenching with 10 mL of sat. aq Na2CO3, the layers were separated and the aqueous layer was extracted with 3 × 10 mL of Et2O. The combined organic layers were concentrated in vacuo and the residue was dissolved in 25 mL of THF. Then, 37% HCl (aq, 4 mL), 0.70 g (12.0 mmol) KF and 5 mL of H2O were added and the mixture was stirred at r.t. until TLC indicated complete conversion (6-24 h). The mixture was washed with 20 mL of brine. The layers were separated and the aqueous layer was extracted with 3 × 20 mL of CH2Cl2. The combined organic layers were dried over MgSO4, filtered and evaporated. Column chromatography (silica gel, EtOAc-hexane = 1:1) provided 0.47 g (58%) 2 as reddish solid. Analytical data for methyl 6-formyl-3-hydroxy-2-methoxybenzoate (2): mp 102-104 °C. 1H NMR (500 MHz, CDCl3): δ = 3.90 (s, 3 H, OMe), 3.98 (s, 3 H, CO2Me), 6.45 (br s, 1 H, OH), 7.11, 7.55 (2 d, J = 8.4 Hz, 2 × 1 H, 4-H, 5-H), 9.79 (s, 1 H, CHO) ppm. 13C NMR (126 MHz, CDCl3): δ = 53.0 (q, CO2Me), 62.5 (q, OMe), 116.6, 129.9 (2 d, Ar), 127.0, 127.6, 144.4, 154.4 (4 s, Ar), 166.9 (s, CO), 189.0 (d, CHO) ppm. IR (KBr): ν = 3150 (O-H), 3005 (=C-H), 2950-2840 (-C-H), 1740, 1660 (C=O), 1600, 1560, 1505 (C=C) cm-1. MS (EI, 80 eV, 170 °C): m/z (%) = 210 (99) [M]+, 195 (57) [M - CH3]+, 182 (46), 179 (71) [M - OCH3]+, 151 (100) [M - CO2CH3]+, 136 (62), 121 (91), 107 (49), 92 (36), 80 (50), 65 (44), 51 (55), 39 (32). Anal. Calcd for C10H10O5 (210.2): C, 57.14; H, 4.80. Found: C, 56.86; H, 4.54.
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9 The constitution of 3 was confirmed by a NOESY experiment.
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Procedure for Heck Reaction 7 → 11: To a solution of 95 mg (0.20 mmol) of 7 and 0.04 mL (0.50 mmol) freshly distilled 3-buten-2-one in 3 mL of dry DMF were added 59 mg (0.21 mmol) of tetra-n-butylammonium chloride, 44 mg (0.52 mmol) of NaHCO3 and 4 mg (0.02 mmol) of palladium(II) acetate. The mixture was stirred at r.t. and the conversion was monitored by TLC. After 72 h, the mixture was diluted with 3 mL of EtOAc and washed with 2 × 3 mL of brine. The layers were separated and the aqueous layer was reextracted with 1 × 5 mL of EtOAc. The combined organic layers were dried over MgSO4, filtered and evaporated. Column chromatography (silica gel, EtOAc-hexane = 1:1) provided 76 mg (91%) 11 as yellow solid. Analytical data for methyl 7-benzyloxy-8-methoxy-1-oxo-6-(3-oxo-but-1-enyl)-1H-isochromene-3-carboxylate (11): mp 169 °C. 1H NMR (500 MHz, DMSO-d
6): δ = 2.23 (s, 3 H, 4′-H), 3.86 (s, 3 H, CO2Me), 3.92 (s, 3 H, OMe), 5.13 (s, 2 H, CH2), 6.77 (d, J = 16.6 Hz, 1 H, 2′-H), 7.33-7.46 (m, 5 H, Ph), 7.53 (s, 1 H, 4-H), 7.55 (d, J = 16.6 Hz, 1 H, 1′-H), 8.01 (s, 1 H, 5-H) ppm. 13C NMR (126 MHz, DMSO-d
6): δ = 27.3 (q, C-4′), 52.9 (q, CO2Me), 61.8 (q, OMe), 76.3 (t, CH2), 112.1 (d, C-4), 117.3, 132.3, 136.37, 136.40, 142.0, 152.2, 155.2 (7 s, Ar, C-3, Ph), 122.2 (d, C-5), 128.70, 128.71, 129.0 (3 d, Ph), 131.5 (d, C-2′), 135.5 (d, C-1′), 156.2, 160.3, 198.0 (3 s, CO) ppm. IR (KBr): ν = 3090-3005 (=C-H), 2950-2850 (-C-H), 1750, 1730, 1675 (C=O), 1620, 1600, 1550, 1500 (C=C) cm-1. MS (EI, 80 eV, 170 °C): m/z (%) = 408 (5) [M]+, 366 (12) [M - C2H2O]+, 275 (12), 91 (100) [C7H7]+, 43 (18), 28 (21). HRMS (EI, 80 eV, 170 °C): m/z calcd for C23H20O7: 408.1209. Found: 408.1224.
