Reaction of octafluorotoluene, 3,5-dichlorotrifluoropyridine, 3-chlorotetrafluoro-yridine and tetrafluoropyrimidine with alkali-metal oximates
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Original research
  • Dr. Waheed J. Jondi

Treatment of octafluorotoluene (2) with approximately one-molar equivalents of the oximates R1R2C = NO~ M+ (R1 = R2=Me;R1 = R2 = Ph; R1 = Me, R2 = Ph;M = Na) (6a-c) in diethyl ether gives 4-(R1R2C = NO)C6F4CF3 (7a-c) as the only isolated products. Corresponding reaction of 3,5-dichlorotrifluoropyridine (3) with the oximates 6a-c affords 4-and 2-(R1R2C = NO)C5F2C12N (8a-c) and (9a-c), respectively (4-/2ratios at −35 °C: 65:35; 30:70; 12:88) ; the lithium oximates (R1 = R2 =Ph ; R1 = Me, R2 = Ph; M = Li) (6d) and (6e) give comparable results. With 3-chlorotetrafluoropyridine (4), treatment with sodium oximate 6c gives 4-(PhCMe = NO)-3-ClC5F3N (10) and 2-(PhCMe = NO)-5ClC5F3N (11) (ratio 44:56 at −35 °C). Such competition between SNAr attack of these alkali-metal oximates at the C-4 and C-2 positions of chlorofluoropyridines 3 and 4 can be rationalized by invoking chelation of an alkali-metal cation with ring nitrogen in the transition state leading to formation of an orthio-quinonoidal σ-complex. Exclusive initial attack at the C-4 ring site appears to occur in the reaction of tetrafluoropyrimidine (5) with oximates 6a and 6c to afford 4-(MeC = NO)C4F3N2 (12a) and 4-(PhCMe=NO)C4F3NN2 (12b), respectively; Some further attack on product 12b by oximate 6c at the C-6 site takes place to give the disubstituted derivative 4,6-(PhCMe=NO)2C4F2N2 (13).

Journal of Fluorine Chemistry, Volume 80, Issue 2, October 1996, Pages 109-116
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