[Li+].CC([N-]C(C)C)C.CCCCCCC.C1COCC1.C(C1C=CC=CC=1)C.[CH3:29][O:30][C:31]1[CH:40]=[C:39]2[C:34]([C:35](=[O:41])[CH2:36][S:37][CH2:38]2)=[CH:33][CH:32]=1.CN(P(N(C)C)(N(C)C)=O)C.C([C:55]([O:57][CH3:58])=[O:56])#N.[NH4+].[Cl-]>C1COCC1>[CH3:58][O:57][C:55]([CH:36]1[C:35](=[O:41])[C:34]2[C:39](=[CH:40][C:31]([O:30][CH3:29])=[CH:32][CH:33]=2)[CH2:38][S:37]1)=[O:56]A 2.0 M solution of LDA in heptane/THF/ethylbenzene (1.61 mL, 3.21 mmol) was added in a dropwise manner to a solution of 7-methoxy-isothiochroman-4-one (0.50 g, 2.57 mmol) in THF (50 mL) at −78° C. under N2. After 30 min at −78° C. HMPA (0.46 g, 2.57 mmol) and methyl cyanoformate (0.27 g, 3.21 mmol) were added and the yellow solution was allowed to stir at −78° C. for 30 min. The solution was then allowed to warm to room temperature and a saturated solution of NH4Cl (100 mL) was added. The slurry was extracted with EtOAc (3×75 mL) and the organic extracts were combined, dried (MgSO4) and concentrated under reduced pressure to provide a bright yellow oil. The oil was purified on silica using medium pressure chromatography (9:1 petroleum ether/EtOAc) to provide 7-methoxy-isothiochroman-4-one-3-carboxylic acid methyl ester as a bright yellow oil (0.51 g, 78%). 1H-NMR (300 MHz, CDCl3) δ 3.73 (s, 2H), 3.83 (s, 3H), 3.85 (s, 3H), 6.67 (d, J=3 Hz, 1H), 6.45 (dd, J=3, 8.7 Hz, 1H), 7.80 (d, J=8.7 Hz, 1H), 12.52 (s, 1H).
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