THE REACTION OF β- AND Γ-LACTONES WITH CHLOROTRIMETHYLSILANE + METAL HALIDES

Great efforts have been made to develop non-saponificative hydrolysis of carboxylates and other esters. Useful methods are so-called SN2-type dealkylation of esters1 and the use of halotrimethylsilanes. Thus iodotrimethylsilane2-4 (ITMS) was originally used and later chlorotrimethylsilane (CTMS) + sodium iodide5 was found to convert alkyl esters into the corresponding trimethylsilyl esters. Also alkyl phosphonates have been cleaved in the same way.6-10 Bromotrimethylsilane (BTMS) does not react with esters.2 However, in a recent note11 it is stated that BTMS cleaves lactones, which prompt us to publish some of our results at this stage of the investigation. It has been found that CTMS is unreactive towards esters and lactones under different conditions studied. However, when β-propiolactone was refluxed with CTMS in acetonitrile with anhydrous sodium chloride, sodium bromide, or potassium iodide present the corresponding trimethylsilyl-3-halopropanoates, IIa-c, were isolated in reasonable yields. Both NaI, H2O, and anhydrous magnesium bromide do cleave β-propiolactone at room temperature to give, after acidification, 3-iodo- and 3-bromopropanoic acids, respectively. Butyrolactone did only react with CTMS in the presence of potassium iodide to give trimethylsilyl-4-iodobutanoate. In the presence of sodium bromide and sodium chloride no reaction took place. In our hands certain lactones such as γ-valerolactone, 2-bromobutyrolactone, thiobutyrolactone, and angelica lactone were totally unreactive. All silyl esters were characterized by MS, NMR, IR, and elementary analyses. Hydrolysis also gave known acids.