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480 g (2.21 mol) of dihydro-α-ionone, 368 g (2.48 mol) of triethyl orthoformate and 480 ml of abs. ethanol are treated dropwise while stirring during 15 minutes with a solution of 34.5 g (0.31 mol) of boron trifluoride etherate in 500 ml of ethanol and the mixture is subsequently heated to an internal temperature of 46°-48° for 60 minutes. After cooling the reaction mixture to room temperature it is stirred with 600 ml of a 10% aqueous sodium hydroxide solution. After extraction with ether and evaporation of the organic phase there are obtained 668.7 g of a slightly yellow liquid which, after flash distillation in a vacuum, gives 480.5 g of crude product (b.p. 45°-73°, 0.07 mbar). After fractionation in a vacuum over a 20 cm Widmer column there are obtained 406.2 g (82.7% of theory) of a slightly yellowish colored liquid (b.p. 48°-67°, 0.06 mbar) which contains the desired bicyclo-nonane in an isomer ratio of exo:endo=2:1

1. temperaturethe mixture is subsequently heated to an internal temperature of 46°-48° for 60 minutes
2. extractionAfter extraction
3. customwith ether and evaporation of the organic phase there
4. customare obtained 668.7 g of a slightly yellow liquid which
5. distillationafter flash distillation in a vacuum