FACILE PREPARATION OF ACETALS AND ENOL ETHERS DERIVED FROM 1-ARYLPIPERIDIN-4-ONES

When primary aromatic amines 6 are heated under reflux with slight exc esses each of crude 1,5-dichloropentan-3-one 4 and toluene-4-sulfonic acid monohydrate in dry methanol solution, and an excess of trimethyl orthoformate is then added to the reactants, the corresponding 1-arylp iperidin-4-one dimethyl acetals 9 are obtained in good (74-81%) overal l yields, The dimethyl acetals 9 undergo hydrolysis in formic acid-wat er (9:1 v/v) at room temperature to give the parent 1-arylpiperidin-4- ones 8 in virtually quantitative yields, When the dimethyl acetals 9 a re allowed to react with an excess each of N, N-diisopropylethylamine and boron trifluoride-diethyl ether complex in dichloromethane solutio n at 0 degrees C they are converted in good yields into the correspond ing enol ethers 10, which are required as reagents in the solid phase synthesis of oligoribonucleotides.