SYNTHESIS AND PROPERTIES OF FLUOROAZULENES .2. ELECTROPHILIC FLUORINATION OF AZULENES WITH N-FLUORO REAGENTS

1-Fluoro- and 1,3-difluoroazulenes were synthesized for the first time by the electrophilic fluorination of azulenes with N-fluoro reagents. Selective preparation of 1-fluoroazulenes were performed by the fluor ination of methyl azulene-carboxylates, followed by demethoxycarbonyla tion in 100% H3PO4. 2-Substituted azulenes were fluorinated in higher yields. In the H-1 NMR of 1-fluoroazulene, long-range J(FH) values wer e not observed at H-2 and H-8, in contrast to those for 1-fluoronaphth alene. The 1-fluorine atom causes significant bathochromic shifts in t he visible absorption of azulene, due to the so-called +I pi effect.