Chemistry Commons^™

Epoxides, or oxiranes, are among the most versatile intermediates in organic synthesis. Yet very few examples of laboratory experiments involving reactions of epoxides are to be found in lab texts. We have developed a discovery-oriented laboratory experiment that involves the rearrangement of both cis- and trans-stilbene oxides with boron trifluoride etherate. The identity of the product can be easily determined by 1H NMR spectroscopy and, in case of the trans isomer, by preparation of the semicarbazone derivative as well. In spite of the simplicity of the experiment, the element of discovery ensures that student interest and enthusiasm are retained.

Aryl-substituted epoxides and aliphatic epoxides with a tertiary epoxide carbon undergo smooth rearrangement in the presence of 10–50 mol% bismuth(III) oxide perchlorate, BiOClO4•xH2O, to give carbonyl compounds. The rearrangement is regioselective with aryl substituted epoxides and a single carbonyl compound arising from cleavage of benzylic C―O bond is formed. BiOClO4•xH2O is relatively non-toxic, insensitive to air and inexpensive, making this catalyst an attractive alternative to more corrosive and toxic Lewis acids such as BF3•Et2O or InCl3 currently used to effect epoxide rearrangements.