Fluorinated acetylenes. Part 12. Reaction of 3,3,3-trifluoropropynyl-lithium with benzil and α-haloacetophenones

Article abstract of DOI:10.1016/S0022-1139(00)80404-2

Treatment of 3,3,3-trifluoropropynyl-lithium (4) with benzil (2:1 molar ratio) in diethyl ether at -50 deg C, followed by addition of an excess of benzoyl chloride, affords 1-benzoyl-5-benzoyloxy-5-phenyl-2,3-bis(trifluoromethyl)cyclopenta-1,3-diene (11) (61percent) and the 1,4-dialkynyl ester (CF3C<*>C)2CPhO2CPh (1b) (8percent).Similar reaction of the salt 4 with α-chloroacetophenone (2:1 molar ratio) in diethyl ether at -50 deg C, followed by addition of a slight excess of benzoyl chloride, gives the ester CF3C<*>CCPh(CH2CI)O2CPh (14a) (55percent) and a compound considered to be 2,5-diphenyl-2,5-bis(3,3,3-trifluoropropynyl)-1,4-dioxan (15) (30percent).Under the same conditions, α-bromoacetophenone yields the corresponding bromo ester CF3C<*>CCPh(CH2Br)O2CPh (14b) (39percent), 2-phenyl-2-(3,3,3-trifluoropropynyl)oxirane (16) (25percent) and the dialkynyl ester (1b) (7percent).The oxirane 16, conveniently prepared (51percent) by treatment of salt 4 with the bromoketone (1:1 molar ratio) in THF at -60 deg C, on reaction with lithium phenylacetylide followed by addition of benzoyl chloride (c. 1:1:1 molar ratio) in THF at -60 deg C gives a compound identified as 2-phenyl-2-(1-phenyl-5,5,5-trifluoropent-3-en-1-yn-3-yl)oxirane (17) or possibly 2-phenyl-2-(3-phenylprop-2-yn-1-yl)-3-(2,2,2-trifluoroethylidene)oxirane (18) in 28percent yield.