3-Substituted furan can be readily prepared in a single step via a tandem Diels-Alder/ retro Diels-Alder reaction between 4-phenyloxazole and simple alkylacetylenes. 3-Substituted furans are a somewhat difficult class of compounds to prepare. For example, the two most common methods of functionalizing furans (i.e. , metallation reactions and electrophilic additions) show a marked preference for position 2 (or 5) over position 3 (or 4) (vide infra)'. -__ Alternative synthetic approaches which do not involve furans as starting materials have also been reported. In the main these involve modifications of butyrolactone derivatives 3 4 or the cyclization of acyclic precursors . All of these are multi-step processes and are generally not well-suited for large scale preparations of furans. We had hoped to gain easy access to a variety of 3-substituted furans using a strategy which is well-precedented for the synthesis of many heterocyclic systems, i.e., a tandem Diels-Alder/retro Diels-Alder sequence of the type shown below. In principle, such an approach would provide us with the needed flexibility with regard to: (a) accessibility of starting materials, (b) functional group compatability, and (c) overall simplicity. Clearly, however, the success of this approach hinges on the selection of the diene. For maximum generality the diene chosen --'H NMR (6) (CDCl3): 7.64 (d, J=2 Hz, 1), 7.18 (d, J=2 Hz, l), 0.26 (s, 9), 0.21 (s, 9).
In summary, the method described above enables one to produce large quantities of 3-substituted furans in a single step. Further applications of this methodology will be the subject of future reports.