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Synlett 2005(20): 3166-3168  
DOI: 10.1055/s-2005-921929
LETTER
© Georg Thieme Verlag Stuttgart · New York

A Facile Synthesis of Homotriptycenes from Anthranol Derivatives

Derong Cao*a,b, Chunmei Gaoa,c, Herbert Meierd
a LCLC, Guangzhou Institute of Chemistry, Chinese Academy of Sciences, Guangzhou 510650, P. R. of China
b College of Chemistry, South China University of Technology, Guangzhou 510641, P. R. of China
Fax: +86(20)85232903; e-Mail: caodr@gic.ac.cn;
c Graduate School of CAS, Beijing 100039, P. R. of China
d Institute of Organic Chemistry, University of Mainz, 55099 Mainz, Germany
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Publication History

Received 26 August 2005
Publication Date:
28 November 2005 (online)

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Abstract

Substituted trans-10-benzyl-9-anthranols 5a,b and substituted 10,10-dibenzyl-9-anthranol 8e undergo intramolecular cyclization in the presence of formic or oxalic acid to give homotriptycenes 9a,b,e. Depending on the amount of acid used, a competitive 1,4-dehydration to anthracene derivatives 10a,b was observed for 5a,b. The latter process was the only reaction pathway for anthranols that do not possess electron-donating substituents on benzyl moiety (5c,d → 10c,d).

Key words

aromatization - condensation - electrophilic substitution - transannular ring closure

9

As experimental example, the synthesis of 3,5-dimethoxypentacyclo [7.6.6.02,7.010,15.016,17] heneicosa-2,4,6,10,12,14,16,18,20-nonaene (9a) is described here. Compound 3a (342 mg, 1.00 mmol) was hydrogenated overnight at ambient temperature in 18 mL EtOAc and 6 mL MeOH in the presence of 5% Pd/C (380 mg). The mixture was filtered through silica gel and the volatile parts removed in vacuo. The residue was dissolved in 4 mL diglyme and treated for 30 min with NaBH4 (120 mg, 3.17 mmol), before 2 mL MeOH were added dropwise. After further 10 min stirring, 60 mg (1.59 mmol) NaBH4 was added and the reaction mixture stirred at r.t. overnight. All these procedures after the reaction with H2 were performed in a N2 atmosphere. Dropwise addition of oxalic acid led to pH 2. After 1 h stirring H2O was slowly added. A solid precipitated which was purified by column chromatography [30 × 3 cm SiO2, PE (bp 40-70 °C)-EtOAc, 30:1]. Colorless crystals of 9a (222 mg, 68% total yield related to 3a) were obtained which melted at 165 °C. 1H NMR (300 MHz, CDCl3): δ = 3.21 (d, 3 J = 2.6 Hz, 2 H, 8-H), 3.63 (s, 3 H, OCH3), 3.89 (s, 3 H, OCH3), 4.19 (t, 3 J = 2.6 Hz, 1 H, 9-H), 5.69 (s, 1 H, 1-H), 6.00 (d, 4 J = 1.8 Hz, 1 H, 4-H), 6.22 (d, 4 J = 1.8 Hz, 1 H, 6-H), 7.09-7.14 (m, 4 H, aromat. H), 7.31-7.35 (m, 4 H, aromat. H). 13C NMR (75 MHz, CDCl3): δ = 37.4, 41.9, 45.6, 55.1, 56.1, 96.6, 107.5, 125.1, 125.6, 126.2, 126.2, 141.1, 144.7, 123.0, 136.7, 156.4, 158.5. FD-MS: m/z (%) = 328 (100) [M+]. Anal. Calcd for C23H20O2 (328.4): C, 84.12; H, 6.14. Found: C, 84.15; H, 6.17. Structure of 9a could be additionally established by a crystal structure analysis, which shall be published later.