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

Abstract

Treatment of 3,3,3-trifluoropropynyl-lithium ( 4) with benzil (2:1 molar ratio) in diethyl ether at −50 °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) (61%) and the 1,4-dialkynyl ester (CF 3CC) 2CPhO 2CPh ( 1b) (8%). Similar reaction of the salt 4 with α-chloroacetophenone (2:1 molar ratio) in diethyl ether at −50 °C, followed by addition of a slight excess of benzoyl chloride, gives the ester CF 3CCPh(CH 2Cl)O 2CPh ( 14a) (55%) and a compound considered to be 2,5-diphenyl-2,5-bis(3,3,3-trifluoropropynyl)-1,4-dioxan ( 15) (30%). Under the same conditions, α-bromoacetophenone yields the corresponding bromo ester CF 3CCCPh(CH 2Br)O 2CPh ( 14b) (39%), 2-phenyl-2-(3,3,3-trifluoropropynyl)oxirane ( 16) (25%) and the dialkynyl ester ( 1b) (7%). The oxirane 16, conveniently prepared (51%) by treatment of salt 4 with the bromoketone (1:1 molar ratio) in THF at −60 °C, on reaction with lithium phenylacetylide followed by addition of benzoyl chloride ( c. 1:1:1 molar ratio) in THF at −60 °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 28% yield.