Journal of Fluorine Chemistry, 56 (1992) zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONM 359-371 359 Some reactions of 3,4-bis(trifluoromethyl)furan and its precursor, 2,3-bis(trifluoromethyl)-7-oxabicyclo [ 2,2,1 lhepta- 2,5-diene: novel isocoumarin formation from thermal reaction of the furan with ethyl propynoate” Aliyu B. Abubakar, Brian L. Booth, Nadia N. E. Suliman (in part) and Anthony E. Tipping** Chemistry zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Department, zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Unzvemity of Manchester Institute of Science and Technology, Manchester M60 IQD YVK) (Received August 12, 1991; accepted November 7, 1991) zyxwvutsrqponmlkjihgfedcbaZYX Abstract Thermolysis at 450 “C of 2,3-bis(trifluoromethyl)-7-oxabicyclo[2,2,l]hepta-2,5-diene (2) gives 3,4-bis(trifluoromethyl)furan (1). Treatment of oxanorbornadiene (2) with triflic acid (m CH&la under reflex) and then with water affords a mixture of 2,3- bis(trifluoromethyl)phenol (4) (69/o), tns-(6-tnfluoromethylsalicylide) (5) (45%) and 2-trifluoromethyl-6-hydroxybenzoic acid (6) (16%); analogous reaction with cont. sulphunc acid gives only the phenol 4 (44%). Die&Alder reaction either of furan 1 with dimethyl acetylenedicarboxylate (DMAD) or of dimethyl 3,4-furandicarboxylate with hexafluorobut-2-yne gives the oxanorbornadiene (8) (ca. 80%). In contrast, reaction of furan 1 with ethyl propynoate (EP) (1:l molar ratio) at 150 “C affords a mixture of ethyl 6,7-bls(triIluoromethyl)isocoumarin-3-carboxylate (12) (52%) and its 4-carboxylate isomer 13 (9%), presumed to arise via a novel Diels-Alder cycloaddition of the dienophile EP to the C=C-C=O system of the 1: 1 adduct ethyl 2,3-bis(trifluoromethyl)-7-oxabicyclo[2,2,l]hepta-2,5-diene-5-carboxylate (14). Diene 14 is conveniently prepared (93%) by the reaction of a large excess of hexafluorobut-2-yne with ethyl 3-furoate at room temperature, and when heated with EP (1:l molar ratio) at 150 “C, the isocoumarin 12 (84%) is obtained; at 60 “C, however, 14 decomposes to give furan 1 and EP. Introduction Furans have found wide use in synthesis as the diene component in Diels-Alder cycloadditions. Oxanorbornadienes, formed by such reactions with alkynes, can be ring-opened with Lewis or protic acids to afford phenols [ 2, 31 or deoxygenated to give benzenes, e.g. with LiAlH,/EtaN/THF [ 41. Also certain 3- and 3,4-substituted furans, which cannot be made straight- forwardly by other methods, have been synthesised from 2- and 2,3-substituted *See ref. 1. **Author to whom correspondence should be addressed. 0022-l 139/92/$5.00 0 1992 - Elsevler Sequoia. AI1 rights reserved