Fluorination of fluorene (1) with caesium fluoroxysulfate (CFS), 2,6-dichloro-1-fluoropyridinium tetrafluoroborate (FP-B800) and 1-fluoro-4-hydroxy-1,4-diazoniabicyclo[2.2.2]- octane bis(tetrafluoroborate) (Accufluor NFTh) occurred only on the aromatic ring in the position ortho and para to the biphenyl central bond with the ratio 2-fluoro- (2a) vs 4-fluorofluorene (2b) 1.7-2.4:1. Regioselectivity of fluorination of both open-chain analogues - diphenylmethane (3a) and biphenyl (3b) was different and more ortho-fluorinated product was formed. Furthermore, the reaction of diphenylmethane (3a) with CFS occurred also on central carbon forming benzophenone (6) and fluorodiphenylmethane (7), while fluorination with FP-B800 and Accufluor NFTh occurred only at the aromatic ring. Similar effect of the structure of fluorinating reagent on the regioselectivity was also observed with dibenzofuran (8) and its open-chain analogues diphenyl ether (10) and biphenyl (3b), where the regioselectivity of fluorination with CFS (1- (9a):2- (9b):3- (9c) = 27:46:27) was similar to fluorination with Selectfluor. Product distribution of fluorination of fluorene (1) and dibenzofuran (8) with CFS is similar to nitration and is in accordance with the calculated HOMO electron density, which indicates the presence of the electron transfer pathway.
对于
氟化反应,使用
氟氧
硫酸铯(CFS)、2,6-二
氯-1-
氟吡啶四
氟硼酸盐(FP-B800)和1-
氟-
4-羟基-1,4-二
氮杂双环[2.2.2]-
辛烷双(四
氟硼酸盐)(Accufluor NFTh)仅在
芴分子的芳香环上发生,位置为
联苯中心键的邻位和对位,生成
2-氟芴(2a)和4-
氟芴(2b)的比例为1.7-2.4:1。对于开链类似物-二苯
甲烷(3a)和
联苯(3b)的
氟化反应选择性不同,更多的邻位
氟化产物被形成。此外,二苯
甲烷(3a)与CFS的反应也发生在中心碳上,生成苯并酮(6)和
氟代二苯
甲烷(7),而与FP-B800和Accufluor NFTh的
氟化反应仅发生在芳香环上。
氟化试剂结构对反应选择性的影响也在
二苯并呋喃(8)及其开链类似物
二苯醚(10)和
联苯(3b)中观察到,使用CFS的
氟化选择性(1-(9a):2-(9b):3-(9c)= 27:46:27)类似于Selectfluor的
氟化选择性。
芴(1)和
二苯并呋喃(8)与CFS的
氟化产物分布类似于硝化反应,并与计算的HOMO电子密度一致,表明存在电子转移途径。