A new efficient route to 2-substituted azulenes based on sulfonyl group directed lithiation.
Directed lithiation of p-tolyl 1-azulenyl sulfone (1) at the 2-position of the azulenyl group was achieved by using lithium 2,2,6,6-tetramethylpiperidide (LTMP). The azulenyllithium thus generated could be efficiently trapped with various electrophiles to form 2-substituted derivatives 2 in moderate to good yields. p-Tolyl 2-trimethylsilyl-1-azulenyl sulfone (2a) was transformed into cyclic sulfone derivative 3a through the directed lithiation in the p-tolyl group and subsequent intramolecular ring closure at the 8-position. 2-(Phenylsulfanyl)-1-azulenyl p-tolyl sulfone (2b) suffered from desulfonylation to form 2-phenylsulfanylazulene (4). The Suzuki coupling reaction of 2-iodo-1-azulenyl p-tolyl sulfone (2d) with arylboronic acids followed by desulfonylation efficiently gave 2-arylazulenes 10.
Shibasaki
Toshihisa
T
Graduate School of Medicine, Yamaguchi University, Yamaguchi City 753-8512, Japan.
Ooishi
Takeo
T
Yamanouchi
Nobuhiko
N
Murafuji
Toshihiro
T
Kurotobi
Kei
K
Sugihara
Yoshikazu
Y
D052176:Azulenes / Q000138:chemical synthesis / Q000737:chemistry*; D008094:Lithium / Q000737:chemistry; D018020:Lithium Compounds / Q000737:chemistry*; D009942:Organometallic Compounds; D011725:Pyridines / Q000737:chemistry*; D013450:Sulfones / Q000737:chemistry*; D014297:Trimethylsilyl Compounds / Q000737:chemistry*
D052176:Azulenes; D018020:Lithium Compounds; D009942:Organometallic Compounds; D011725:Pyridines; D013450:Sulfones; D014297:Trimethylsilyl Compounds; C522527:lithium 2,2,6,6-tetramethylpiperidide; C534362:p-tolyl 2-trimethylsilyl-1-azulenyl sulfone; D008094:Lithium