2-Butadienylphenacyloxazolones undergo an intramolecular Diels-Alder reaction to give a tetracyclic species that is a useful intermediate for the synthesis of phenanthridone alkaloids, specifically Pancratistatin. A problem with the synthesis is the lack of a good procedure for the preparation of 2-oxazolone, which is not commercially available. We have shown that sulfuryl chloride reaction with 2-oxazolidinone leads to two chlorooxazolidinones which are separable. They react differently upon heating and low yields of oxazolone are obtained. Better results are obtained by simply heating the crude chlorinated products. Also, over-chlorination to the vicinal dichloride provides an alternate route to oxazolone after reduction with zinc in acetic acid. The overall yield of oxazolone is no better than other literature reports, but these methods avoid the use of chlorine gas and are manageable on a lab scale.
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