A convenient procedure for the synthesis of acetals from α-halo ketones

A study for determining the scope and limitations of a procedure for synthesising ethylene acetals from haloketones is presented. The method uses 1,2-bis(trimethylsilyloxy) ethane, BTSE, as reagent and Nafion(R)-TMS as catalyst. Two procedures have been tested: (A) stoichiometric amounts of the haloketone and BTSE and a catalytic amount of Nafion(R)-TMS were heated to reflux in chloroform solution, and (B) stoichiometric amounts of the reactants and a catalytic amount of Nafion(R)-TMS were heated to 90-100degreesC in the absence of solvent. The following ketones have been tested: 2-bromo-1-phenyl-1-ethanone, 2-bromo-cyclopentenone, 3-bromo-3-methyl-2-butanone, 3-chloro-3-methyl-2-butanone, 1-bromo-3,3-dimethyl-2-butanone, 1-chloro-3,3-dimethyl-2-butanone, 2-bromocyclohexanone, 2-chloro-1-cyclohexyl-1-ethanone, 1,1-dibromo-3,3-dimethyl-2-butanone, 1,3-dibromo-3-methyl-2-butanone, 1,3-dibromo-2-butanone, 1,3-dibromo-2-propanone, 2-chloro-1-phenyl-1-ethanone, and endo-2-bromocamphor. Yields were in the range 57-100% with the exceptions of endo-2-bromocamphor which afforded < 10% yield and the dibromoketones 1,1-dibromo-3,3-dimethyl-2-butanone and 1,3-dibromo-3-methyl-2-butanone for which the method failed. Factors determining the scope and limitations are briefly discussed. Full experimental details and spectroscopic data of the acetals are given.