Caprolactam → 2H-Azepine, 3,4,5,6-tetrahydro-7-methoxy-

To a solution of azepan-2-one (1.13 g, 10.0 mmol) in DCM (10 mL) in a 40 mL screw cap vial was added freshly prepared trimethyloxonium tetrafluoroborate (1.57 g, 10.59 mmol). The resulting suspension was shaken overnight. The reaction was quenched by the addition of saturated aqueous NaHCO3 (5 ml) (caution: vigorous CO2 evolution). More aqueous sodium hydrogen carbonate was added until the aqueous layer reached pH 8. The organic layer was removed and the aqueous layer extracted with DCM (5 mL). Combined organic layers were dried over anhydrous sodium sulfate, filtered and evaporated under reduced pressure to yield (E)-7-methoxy-3,4,5,6-tetrahydro-2H-azepine (1.2 g, 95%) as a clear oil. LCMS (+ESI) m/z 128.2 [M+H]+. 1H-NMR (CDCl3) δ 3.60 (s, 3H), 3.45 (m, 2H), 2.40 (m, 2H), 1.80 (m, 2H), 1.60-1.50 (m, 4H).