Polyfluorinated heterocyclic compounds. Part 29[1]. The synthesis of 4,5,6,7,8-pentafluoro-2H-cyclohepta[b]furan-2-one and its reaction with sodium methoxide.

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Abstract

Pentafluorophenyl propynoate (8), prepared from sodium pentafluorophenate and propynoyl chloride, on flash vacuum pyrolysis through silica gave 4,5,6,7,8-pentafluoro-2H- cyclohepta[b]furan-2-one (9). Treatment of (9) with sodium methoxide in methanol at −70°C produced a mixture of the 4-methoxy-, 5-methoxy-, 6-methoxy-, 7-methoxy- and 8-methoxy-tetrafluoro-2H-cyclohepta[b]furan-2-one compounds (10), (11), (12), (13) and (14) in the ratio 11:18:8:19:44 respectively. Under more forcing conditions, the 4,8- and 5,8-dimethoxy-trifluoro-2H-cyclohepta[b]furan-2-one compounds (15) and (16) respectively were formed. X-ray crystallography identified the 8-methoxy derivative (14), whose fluorine nmr spectrum enabled key resonances to be identified in the parent (9) and subsequently allowed the structures of all the other products to be deduced.

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Cited by (2)

  • Fluorine-containing heterocycles. Part II. Synthesis of perfluoroalkyl heterocycles from carbonyl compounds

    2004, Advances in Heterocyclic Chemistry
    Citation Excerpt :

    A Diels–Alder reaction between hexafluoropropane-2-imine and 2,3-dimethylbutadiene at 100 °C gives an adduct in excellent yield (65JOC1398) (Scheme 18). The reaction of epichlorohydrin with hexafluoroacetone in the presence of catalytic amounts of Bu4NBr affords 2,2-bis(trifluoromethyl)-4(bromomethyl)-1,3-dioxolane 16, which on further treatment with KOH yields 2,2-bis(trifluoromethyl)-4-methylene-1,3-dioxolane 17 (92JPK311) (Scheme 19). The [4+1] cycloaddition of 4,4-bis(trifluoromethyl)-1,3-diazabuta-1,3-diene 18, obtained by a reaction of hexafluoroacetone with an amidine in the presence of a dehydrating agent, to an isonitrile gives 5-(butylimino)-1-(2,6-dimethyl-phenyl)-2-phenyl-4,4-bis(trifluoromethyl)-2-imidazoline 19 in the form of Z and E isomers (92JFC(58)345) (Scheme 20).

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