RAPID AND CONVENIENT TECHNIQUE FOR CONVERTING KETONES INTO THEIR ETHYLENEDIOXY-DERIVATIVES OR TRIMETHYLENEDIOXY-DERIVATIVES, AND FOR MAKING ACETONIDES

The ethylenedioxy-derivatives (ethylene acetals) of unhindered steroid, triterpene, and other ketones can be prepared by running a mixture of the ketone and ethylene glycol in tetrahydrofuran through an acid ion-exchange column and isolating the derivative from the eluate. This technique is particularly appropriate where such compounds are to be subjected to mass spectrometry but can also be used on a larger scale in synthetic sequences where protection of the carbonyl group is desired. The homologous (cyclic trimethylenedioxy-) derivatives, better for the latter purpose in certain cases, can be prepared in the same way, as can the acetonides of 1,3-dihydroxy-compounds.