Pyrolysis reactions of 4-phenyl-2,3,5,6-tetrafluorophenyl prop-2-enyl ether and 4-trifluoromethyl-2,3,5,6-tetrafluorophenyl prop-2-enyl ether: remarkable rearrangement reactions of intramolecular Diels–Alder products.

Add time:07/16/2019    Source:sciencedirect.com

The pyrolyses of 4-phenyl-2,3,5,6-tetrafluorophenyl prop-2-enyl ether (26) under flash vapour phase (FVP) conditions at 350°C and of 4-trifluoromethyl-2,3,5,6-tetrafluorophenyl prop-2-enyl ether (27) on heating in vacuo at 169°C give mixtures of products which include 3-phenyl-2,4,5,7-tetrafluorotricyclo[3.3.1.02,7]non-3-ene-6-one (28), and 3-trifluoromethyl-2,4,5,7-tetrafluorotricyclo[3.3.1.02,7]non-3-ene-6-one (31), respectively, the products of one of the two possible intramolecular Diels–Alder reactions of the Claisen rearrangement intermediates 2. FVP of 26 at 430°C and 27 at 450°C give the bicyclic compounds 7-phenyl-2,5β,6,7aβ-tetrafluoro-3aβ,4,5,7a-tetrahydroinden-1-one (34) and 7-trifluoromethyl-2,5β,6,7aβ-tetrafluoro-3aβ,4,5,7a-tetrahydroinden-1-one (37), respectively. It is proposed that these latter two compounds are formed via two possible intermediates produced by recyclisations of the tethered 2,4,5-trifluoro-3-(substituent)-2,4-cyclohexadienylmethyl fluoroketene (23), itself formed via new retro-cyclisation reactions of 28 and 31, respectively. Also formed from 27 via 31 is 1,2,4β,5,7-tetrafluoro-3-(trifluoromethyl)bicyclo[3.3.1]nona-2,6-dien-8-one (39).

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