Synthesis of 9,10-Diarylanthracenes via Mg(TMP)2·2LiCl-Mediated Benzyne Generation/[4+2] Cycloaddition and Deoxygenation of 9,10-Epoxyanthracene Intermediates
Naoya Miyamoto
a
Graduate School of Pharmaceutical Sciences, Tohoku University, Aoba 6-3, Aramaki, Aoba-ku, Sendai, 980-8578, Japan Email: tokuyama@m.tohoku.ac.jp
,
Yuki Nakazawa
a
Graduate School of Pharmaceutical Sciences, Tohoku University, Aoba 6-3, Aramaki, Aoba-ku, Sendai, 980-8578, Japan Email: tokuyama@m.tohoku.ac.jp
,
Takanori Nakamura
a
Graduate School of Pharmaceutical Sciences, Tohoku University, Aoba 6-3, Aramaki, Aoba-ku, Sendai, 980-8578, Japan Email: tokuyama@m.tohoku.ac.jp
a
Graduate School of Pharmaceutical Sciences, Tohoku University, Aoba 6-3, Aramaki, Aoba-ku, Sendai, 980-8578, Japan Email: tokuyama@m.tohoku.ac.jp
,
Sota Sato
b
Department of Chemistry, The University of Tokyo and JST,
ERATO, Isobe Degenerate π-Integration Project, Hongo 7-3-1, Bunkyo-ku, Tokyo, 113-0033, Japan
,
Zhe Sun
b
Department of Chemistry, The University of Tokyo and JST,
ERATO, Isobe Degenerate π-Integration Project, Hongo 7-3-1, Bunkyo-ku, Tokyo, 113-0033, Japan
b
Department of Chemistry, The University of Tokyo and JST,
ERATO, Isobe Degenerate π-Integration Project, Hongo 7-3-1, Bunkyo-ku, Tokyo, 113-0033, Japan
,
Hidetoshi Tokuyama*
a
Graduate School of Pharmaceutical Sciences, Tohoku University, Aoba 6-3, Aramaki, Aoba-ku, Sendai, 980-8578, Japan Email: tokuyama@m.tohoku.ac.jp
› Author AffiliationsThis work was financially supported by JSPS KAKENHI Grant Numbers 16H01127, 16H00999, 17K05773, 16K04864, a Grant-in aid for Scientific Research (A) (26253001), JST ERATO (JPMJER1301), MEXT (Interdepartmental Doctoral Degree Program for Multidimensional Material Science Leaders), and JSPS predoctoral fellowship (for N.M.).
A new synthetic route to functionalized 9,10-diarylanthracenes has been developed. 9,10-Epoxyanthracene intermediates were prepared by [4+2] cycloaddition of 1,3-diarylisobenzofuran with a variety of functionalized benzyne intermediates, which were obtained by Mg(TMP)2·2LiCl-mediated benzyne generation. For the cleavage of the resultant 9,10-epoxyanthracene intermediates, we developed mild deoxygenation conditions using a combination of trifluoroacetic acid and Et3SiH. The utility of this sequence was demonstrated by application to the synthesis of 5,7,12,14-tetraphenylpentacene.
17 A preliminary result of [4+2] cycloaddition of 1,3-(4-bromophenyl)isobenzofuran with benzyne generated by treatment of PhOTf with Mg(TMP)2·2LiCl was reported by our group (ref. 16b).
18A Gram-Scale Preparation of tert-Butyl 9,10-Diphenyl-9,10-epoxy-2-anthracenecarboxylate (3e)
A flame-dried 500 mL three-necked round-bottomed flask equipped with a 200 mL dropping funnel, a magnetic stirring bar, a rubber septum, and an inlet adapter with a three-way stopcock was charged with 1,3-diphenylisobenzofuran (2a, 2.16 g, 8.00 mmol), dry THF (20.0 mL), and tert-butyl 4-(trifluoromethylsulfonyloxy)benzoate (1e, 1.23 g, 3.77 mmol). After cooling to –78 °C, Mg(TMP)2·2LiCl (0.16 M in THF, 130 mL, 20 mmol) was added dropwise to the flask, and the resulting mixture was stirred at –78 °C for 1 h. The flask was then immersed in an ice bath, and the mixture was stirred for 11 h, after which time TLC (hexanes–EtOAc = 2:1) indicated complete consumption of tert-butyl 4-(trifluoromethylsulfonyloxy)benzoate (1e). The reaction was quenched by addition of sat. aq NH4Cl, and the aqueous layer was extracted with EtOAc three times. The combined organic extracts were successively washed with H2O and brine, dried over anhydrous Na2SO4, and filtered. The organic solvents were removed under reduced pressure to give a crude epoxyanthracene, which was purified by flash column chromatography on silica gel (hexanes–dichloromethane = 1:1) to afford 3e (1.53 g, 3.43 mmol, 91%) as a white solid. Rf = 0.18 (hexanes–dichloromethane = 1:1). The spectral data of 3e were in complete agreement with those reported in the literature (ref. 19).
19
Uchiyama M.
Kobayashi Y.
Furuyama T.
Nakamura S.
Kajihara Y.
Miyoshi T.
Sakamoto T.
Kondo Y.
Morokuma K.
J. Am. Chem. Soc. 2008; 130: 472
21tert-Butyl 9,10-Diphenyl-2-anthracenecarboxylate (4e)
A 10 mL test tube equipped with a magnetic stirring bar and a cap was charged with tert-butyl 9,10-diphenyl-9,10-epoxy-2-anthracenecarboxylate (3e, 100 mg, 224 μmol), wet CH2Cl2 (448 μL), Et3SiH (53.7 μL, 336 μmol), and TFA (20.0 μL, 269 μmol). The mixture was stirred for 23 h, after which time TLC (hexanes–EtOAc = 3:1) indicated complete consumption of tert-butyl 9,10-diphenyl-9,10-epoxy-2-anthracenecarboxylate (3e). The reaction was quenched by addition of H2O, and the aqueous layer was extracted with CH2Cl2 three times. The combined organic extracts were successively washed with sat. aq NaHCO3and brine, dried over anhydrous Na2SO4, and filtered. The organic solvents were removed under reduced pressure to give a crude anthracene, which was purified by flash column chromatography on silica gel (hexanes–CH2Cl2 = 4:1) to afford 4e (85.3 mg, 198 μmol, 88%) as a pale yellow solid. Rf = 0.73 (hexanes–EtOAc = 3:1). For the spectral data of 4e, see the Supporting Information.
22 In the case of LiTMP was used as the base, the yield (14%) was lower than using Mg(TMP)2·2LiCl as the base.
23
Athans AJ.
Briggs JB.
Jia W.
Miller GP.
J. Mater. Chem. 2007; 17: 2636
