[Mn]([O-])(=O)(=O)=[O:2].[K+].[CH:7]1([O:12][C:13]2[CH:14]=[C:15]([CH:18]=[CH:19][C:20]=2[O:21][CH3:22])[CH:16]=[O:17])[CH2:11][CH2:10][CH2:9][CH2:8]1.Cl>[Br-].C([N+](CCCC)(CCCC)CCCC)CCC.O.N1C=CC=CC=1>[CH:7]1([O:12][C:13]2[CH:14]=[C:15]([CH:18]=[CH:19][C:20]=2[O:21][CH3:22])[C:16]([OH:2])=[O:17])[CH2:8][CH2:9][CH2:10][CH2:11]1
A solution of tetrabutylammonium bromide (111.68 g, 0.336 moles) in water (400 ml) was added under stirring to a solution of potassium permanganate (53.1 g, 0.336 moles) in water (1 l). The obtained solid was separated by filtration, washed with water and dissolved in 500 ml of pyridine. This solution was dropped into one of crude 3-cyclopentyloxy-4-methoxy benzaldehyde (obtained as described in J. Med. Chem., 1995, 38, page 4851) (74 g, 0.336 moles) in pyridine (200 ml), under stirring in water/ice. At the end 3 l of ice were added and it was acidified by dropping 850 ml of 12N HCl. The stirring was kept for further 1.5 hours, then the solid was separated by filtration and extracted under stirring for 30 minutes with ethyl acetate (2 l). The residual solid was removed and the mother liquors were further extracted with ethyl acetate (2×700 ml). The organic phases were washed with water, dried on sodium sulphate and concentrated to small volume to give 53.2 g of the title compound (yield: 67%).
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