Fluorinated acetylenes. Part 10. Cycloadditions of α,α-bis(3,3,3-trifluoropropynyl) benzyl benzoate and 1,1-bis(3,3,3-trifluoropropynyl) ethyl ethanoate with furan and cyclopentadiene

Abstract

Reaction between furan and the dialkynyl ester (CF₃CC)₂CPhO₂CPh 1a in dichloromethane at 50 °C gave four rearranged 1 : 1 adducts, (Z)-5-(α-benzoyloxybenzylidene)-1,4-bis(trifluoromethyl)-8-oxa-tricyclo[4.3.0.0^2,9]nona-3,6-diene 11a(major product), 4-benzoyloxy-3,8-bis(trifluoromethyl)-1,1a,-2,8c-tetrahydro-4H-1,2,8b-epoxymethenocyclopropa[c]fluorene 15, the corresponding 3H-compound 16 and 8,9-dibenzoyl-4,7-bis(trifluoromethyl)-2-oxatetracyclo[4.3.0.0.^3,50^4,9]non-7-ene 13avia the common intermediate 2-benzoyloxy-2-phenyl-4,10-bis(trifluoromethyl)-7-oxapentacyclo[4.4.0.0.^1,3-0.^5,90^8,10]dec-3-ene 8a formed from the Diels–Alder adduct by intramolecular (_π2_s+_π2_s+_π2_s) cyclo-addition. The corresponding reaction with the ester (CF₃CC)₂CMeO₂CMe 1b gave analogously the diketone 13b(major product) and a mixture of the (E)- and (Z)-isomers of the triene 11b; a 2 : 1 adduct, 4-acetoxy-3-methyl-5,11-bis(trifluoromethyl)-8,1 5-dioxahexacyclo[10.2.1.0.^2,110.^4,90.^5,70.^6,10]-pentadeca-2,13-diene 10 was also isolated. A mixture of cyclopentadiene and the ester 1a(2 : 1 molar ratio), heated at 50 °C, yielded mainly the bis-Diels–Alder adduct α,α-bis(3-trifluoromethyl-bicyclo[2.2.1]hepta-2,5-dien-2-yl)benzylbenzoate 7a, together with the rearranged 1 : 1 adduct, diketone 13c. Similarly, the major product from the reaction of an excess of cyclopentadiene with ester 1b at 50 °C was the bis-Diels-Alder adduct 7b, but a 1 : 1 molar ratio of reactants at 20 °C gave the mono Diels-Alder adduct 1-(3-trifluoromethylbicyclo[2.2.1 ]hepta-2,5-dien-2-yl)-1-(3,3,3-trifluoropropynyl)ethyl ethanoate 6d in high yield. The bis adduct 7a was stable at 50 °C, but the mono adduct 6d underwent slow intramolecular (_π2_s+_π2_s+_π2_s) cycloaddition, cf., the furan reactions, and the intermediate 8d so formed rearranged to a mixture of 8,9-diacetyl-4,7-bis(trifluoromethyl)-tetracyclo[4.3.0.0.^3,50^4,9]non-7-ene 13d and 1-acetoxy-1-[4,7- bis(trifluoromethyl)tetracyclo-[4.3.0.0.^3,50^4,9]non-7-en-9-yl]ethene 18. In the presence of traces of water, the ketone 13d was only a minor product with the major products being the substituted ethene 18 and two diastereoisomers of 1-acetoxy-1-[4,7-bis(trifluoromethyl)tetracyclo[4.3.0.0.^3,50^4,9]non-7-en-9-yl]ethanol 19.