RADICAL ARYLATION REACTIONS OF 4,6,8-TRIMETHYLAZULENE

The synthesis of 1- and 2-aryl-substituted (aryl = Ph, 4-NO2-C6H4 and 4-MeO-C6H4)4,6,8-trimethylazulenes (4 and 3, respectively) in moderate yields by direct arylation of 4,6,8-trimethylazulene (8) with the corresponding arylhydrazines 13 in the presence of Cu-II ions in pyridine (see Scheme 4) as well as with 4-MeO-C6H4Pb(OAc)(3) (16) in CF3COOH (see Scheme 5) is described. With 13, also small amounts of 1,2- and 1,3-diarylated azulenes (see 14 and 15, respectively, in Scheme 4) are formed. The 4-methoxyphenylation of 8 with 16 yielded also the 1,1'-biazulene 17 in minor amounts (see Scheme 5). 4,6,8-Trimethyl-2-phenylazulene (3a) was also obtained as the sole product in moderate yields by the reaction of sodium phenylcyclopentadienide (1a) with 2,4,6-trimethylpyrylium tetrafluoroborate (2) in THF (Scheme 1). The attempted phenylation of 8 as well as of azulene (9) itself with N-nitroso-N-phenylacetamide (10) led only to the formation of the corresponding 1-(phenylazo)-substituted azulenes 12 and 11, respectively (Scheme 3).