Ethyl orthoformate → 3-(1'-Diethoxymethyl-1',2'-dihydro-2'-oxospiro[cyclohexane-1,3'-[3H]indol]-5'-yl)-5-fluorobenzonitrile

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A solution of 3-(1′,2′-dihydro-2′-oxospiro[cyclohexane-1,3′-[3H]indol]-5′-yl)-5-fluorobenzonitrile (1.0 eq, 0.27 g, 0.84 mmol) in triethylorthoformate (2 mL, 12 mmol) was heated to 150° C. for 1 h. The reaction mixture was allowed to cool, the excess triethylorthoformate was removed in vacuo, and the residue was purified by flash column chromatography on silica gel (eluting with 10% EtOAc/hexane) to give the title compound (0.2 g, 56%) as a white powder, mp 146° C. 1H NMR (DMSO-d6; 400 MHz) δ 1.13 (t, 6H, J=7 Hz), 1.60-1.96 (m, 10H), 3.48 (m, 2H), 3.66 (m, 2H), 6.17 (s, 1H), 7.35 (d, 1H, J=8.3 Hz), 7.68 (dd, 1H, J=2.0, 8.3 Hz), 7.77 (ddd, 1H, J=1.3, 2.4 Hz), 7.89 (d, 1H, J=2.0 Hz), 7.92 (dt, 1H, J=2.4, 10.5 Hz)8.08 (dd, 1H, J=1.3, 2.9 Hz). MS ((+)−EI) m/z 422 [M+]. Anal. Calcd for C25H27FN2O3: C, 71.07; H, 6.44; N, 6.63. Found: C, 70.75; H, 6.48; N, 6.52.

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