[CH:1]([C:3]1(O)[CH2:7][CH2:6][CH2:5][CH2:4]1)=[CH2:2].C[O:10][C:11]([CH3:13])=[CH2:12].OP(O)(O)=O.N#N>CC(OC)(C)C.C(N(CC)CC)C>[C:3]1(=[CH:1][CH2:2][CH2:12][C:11](=[O:10])[CH3:13])[CH2:7][CH2:6][CH2:5][CH2:4]1A 600 ml autoclave containing a mixture of 1-ethenyl-cyclopentanol (172.0 g; 1.54 mol), isopropenyl methyl ether (218.8 g; 3.04 mol), triethylamine (1.65 ml) and 85% H3PO4 (0.72 ml) was pressurized with N2 at 2 bar and heated up to 125° C. An increase of the pressure to 7 bar was observed. After 14 hours stirring, the autoclave was cooled down to room temperature and depressurized. MTBE (1.5 l) was added to the mixture, washed with H2O (4×25 ml) until neutral pH, dried (MgSO4) and concentrated. Distillation (61° C./0.1 torr) yielded 161.3 g (69% yield) of 5-cyclopentylidenepentan-2-one.
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