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Synlett 2005(12): 1951-1953  
DOI: 10.1055/s-2005-871925
LETTER
© Georg Thieme Verlag Stuttgart · New York

Heteroaryl Radicals: A Furyl Radical in the Synthesis of the Tricyclic ­Framework of Eremophilane Sesquiterpenoids

Sajal K. Mal, Surajit Some, Jayanta K. Ray*
Department of Chemistry, Indian Institute of Technology, Kharagpur 721302, India
Fax: +91(322)2282252; e-Mail: jkray@chem.iitkgp.ernet.in;
Further Information

Publication History

Received 3 May 2005
Publication Date:
07 July 2005 (online)

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Abstract

Studies on the intramolecular addition of thieno and ­furan radicals to alkenyl groups are reported. The radicals undergo a 6-endo-trig selective cyclization to alkenyl systems resulting in a linearly annulated tricyclic moiety.

Key words

radical reactions - cyclizations - furans - terpenoids

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Radical cyclization of 6 and 12 with Bu 3 SnH To a solution of 6 or 12 (50 mg, 0.227 mmol or 0.245 mmol) in degassed anhyd benzene (30 mL) heated under reflux were added Bu3SnH (1.5 equiv) and AIBN (5 mg, 0.02 mmol) in degassed anhyd benzene (20 mL) slowly by syringe pump. The addition of Bu3SnH was carried out over 2 h and the mixture was heated under reflux for 8 h. The solvent was removed under reduced pressure, Et2O (20 mL) and a sat. aq solution of KF (20 mL) were added to the residue; the whole mixture was stirred at r.t. for 24 h. The organic phase was separated, washed with brine, dried, and concentrated. Purification was carried out by chromatography(hexane).

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Spectral data of representative compounds.
5,5-Dimethyl-4,4a,5,6,7,8,8a,9-octahydronaphtho[2,3- b ]thiophene ( 7) 1H NMR (CDCl3, 200 MHz): δ = 0.88 (s, 3 H), 0.96 (s, 3 H), 1.25-1.59 (m, 8 H), 2.27-2.41 (m, 2 H), 2.62-2.88 (m, 2 H), 6.73 (d, 1 H, J = 5.11 Hz), 7.02 (d, 1 H, J = 5.11 Hz); MS (EI, 70 ev): m/z = 220 (M+); Anal. Calcd for C14H20S: C, 76.30; H, 9.15. Found: C, 76.45; H, 9.25.
8,8-Dimethyl-4,4a,5,6,7,8,8a,9-octahydronaphtho[2,3- b ]furan ( 13) 1H NMR (CDCl3, 200 MHz): δ = 0.88 (s, 3 H), 0.96 (s, 3 H), 1.21-1.58 (m, 8 H), 1.71-2.71 (m, 4 H), 6.15 (br s, 1 H), 7.22 (br s, 1 H); ESI-MS: m/z = 205.12 [M + H]+; Anal. Calcd for C14H20O: C, 82.30; H, 9.87. Found: C, 82.65; H, 9.76.