a compound the lowest singlet excited state of the third compound preferably has a pi pi nature this compound may further have a protecting group 2 75 g of 2h dihydropyran and 0 74 g of pyridinium p toluenesulfonate are dissolved in 30 0 g of methylene chloride 2 0 g of bis 4 methoxy phenyl methanol compound 2 dissolved by 8 0 g of methylene chloride is added dropwise to the mixture containing 2h dihydropyran and pyridinium p toluenesulfonate over 30 minutes after that the mixture is stirred at 25 degrees celsius for 3 hours since then the mixture is further stirred after addition of 3 aqueous solution of sodium carbonate and then extracted with 20 0 g ethyl acetate the organic phase is washed with water thereafter ethyl acetate is distilled away thereby 1 99 g of 2 bis 4 methoxy phenyl methoxy tetrahydropyran is obtained 2 0 g of 4 4 u2032 dimethoxy benzophenone 0 05 g of bismuth iii trifluoromethanesulfonate and 5 7 g of trimethyl orthofomate are dissolved in 5 0 g of methanol the mixture is stirred at reflux temperature for 42 hours since then the mixture is cooled to 25 degrees celsius and further stirred after addition of 5 aqueous nahco 3 solution.