To a solution of 2,5,9-trimethyl-11-(2,6,6-trimethyl-1-cyclohexen-1-yl)-2,4,6,8,10-undecapentaene-1-ol (1.6 g, 5 mmol), 106 g (10 mmol) of trimethyl orthoformate and 160 mg (5 mmol) of dry methanol in 5 ml of dry THF is added dropwise a solution of 40 μL of trifluoroacetic acid in 1 ml of dry THF over a 1 minute period at room temperature. After overnight standing, the reaction mixture is poured into cold aqueous 5% NaHCO3 and extracted with chloroform three times. The combined organic extract is washed with water, dried over Na2SO4 and evaporated in vacuo to give a residue, which is purified by HPLC (4% ether in hexane, silica gel column) to afford of 1-methoxy-2,5,9-trimethyl-11-(2,6,6-trimethyl-1-cyclohexen-1-yl)-2,4,6,8,10-undecapentaene as an oil.
