Stereoselective Synthesis and Thermal Behavior of (Z)-Epoxyhexenynes: A Sinple and General Route to 2-Vinylfurans

An efficient approach for the synthesis of 2,3-disubstituted furans 3is described by using the thermally induced rearrangement of epoxyhexenynes (k-1) which are prepared by stereoselective synthesis of the (7.)-pentenynals 10 and subsequent Darzens reaction.Recently we communicated first results on the unexpected formation of 2-vinylla furans by short-time thermolysis of three 1-phenylepoxyhex-(32)-ene-5-ynes .This observation prompted us to further investigations in order to gain more insight into the mechanism of the unprecedented rearrangement and to elaborate the preparative aspects of the reaction as a possible alternative to specifically 2 substituted furans .In this contribution we report on the straightforward synthesis of several derivatives of furan bearing bulky substituents not only at the vinyl group but also in 3-position (see structures 2 and 3 ) .The epoxyhexenynes &-1, comprising the essential (7.)-geometry of the central double bond, have been selected as appropriate starting materials.In addition to 1 2 preparative reasons, the substituents R / R were introduced to disclose steric and/or electronic effects on the course of the rearrangement and (at least in the case of CH3, iC3H7, nC H for enabling intra-(or inter-) molecular H-shifts