Total synthesis of vibsanol, a benzofuran-type lignan

Tetrahedron Letters

Volumn 40, Issue 22, 1999, Pages 4211-4214

  Sakai, Atsushi ^a   Aoyama, Toyohiko ^a   Shioiri, Takayuki ^a  

^a NAGOYA CITY UNIVERSITY   (Japan)

Author keywords

[No Author keywords available]

Indexed keywords

ALKYNE; AMMONIUM FLUORIDE; BENZOFURAN DERIVATIVE; DITERPENE; HUMULENE; LIGNAN DERIVATIVE; PARAFORMALDEHYDE; TETRABUTYLAMMONIUM; UNCLASSIFIED DRUG; VANILLIN; VIBSANOL;

ARTICLE; CYCLIZATION; DRUG SYNTHESIS;

CAPRIFOLIACEAE; VIBURNUM; VIBURNUM AWABUKI;

EID: 0033612268     PISSN: 00404039     EISSN: None     Source Type: Journal    
DOI: 10.1016/S0040-4039(99)00714-5     Document Type: Article

References (20)

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16. 4, filtered, and concentrated in vacuo. The residue was purified by silica gel chromatography (hexane : EtOAc = 6 : 1 → 4 :1) to afford the recovered 4 (129 mg, 29 %) and the desired 2 (306 mg, 60 %) as a viscous yellow oil.
17. The use of acetonitrile instead of THF gave only the protonated benzofurans and no hydroxymethylation products were obtained. See ref. 4.
18. Cf. ref. 4. 2-Phenylbenzofuran was also obtained in 16 % yield.
19. To a stirred mixture of paraformaldehyde (34 mg, 90 % purity, 1.0 mmol) and powdered 4 Å molecular sieves (400 mg, dried over at 180 °C for 4 h under reduced pressure prior to use) in THF (1 ml) was added TBAF (0.18 ml, 0.49 M in THF, 0.087 mmol) at room temperature under argon, and the mixture was stirred at this temperature for 3 h. Then the alkyne 2 (43 mg, 0.067 mmol) in THF (1 ml) was added dropwise to the mixture, which was stirred at 50 °C for 3 h. After cooling to room temperature, the reaction mixture was filtered through a pad of Celite to remove the molecular sieves. The filtrate was concentrated in vacuo, and the residue was purified by silica gel chromatography (hexane : EtOAc = 4 : 1 → 2 :1) to afford the protonated 9 (7 mg, 20 %) as a yellow oil and the desired 8 (25 mg, 67 %) as a colorless oil.
20. Unfortunately, when O-methoxymethyl groups were employed instead of O-1-ethoxyethyl groups, the deprotection of the final step was unsuccessful for decomposition under the normal reaction conditions (e.g., 0. 1N HCl, TFA, cat.HCl/NaI/acetone, TMSBr, B-bromocatecholborone, triphenylmethyl tetrafluoroborate).