Synthesis of the Proposed Structure of Afzeliindanone

Abstract

A synthesis of the proposed structure of afzeliindanone was achieved by using an alkyne [2+2+2]-cyclotrimerization as a key step. The data for the synthetic material were found not to match those for the natural material, indicating a structural misassignment.

Key words

alkynes - cyclotrimerization - indanones - rhodium catalysis - afzeliindanone

• References and Notes

• 1 Okpekon T, Millot M, Champy P, Gleye C, Yolou S, Bories C, Loiseau P, Laurens A, Hocquemiller R. Nat. Prod. Res. 2009; 23: 909

For another example of an indanone natural product, see:
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• 6 In some runs, alkyne 6 was contaminated with the product of Glaser coupling of the pentynol. This could be easily separated after the subsequent Swern oxidation.
• 7 4-(1-Hydroxy-2,3-dihydro-1H-inden-4-yl)-2-methoxyphenyl Methanesulfonate (8) A solution of diyne 2a (500 mg, 1.62 mmol) in EtOH (8 mL) was purged with N₂ gas for 10 min and then with acetylene gas for 30 min. A solution of RhCl(PPh₃)₃ (150 mg, 0.162 mmol, 10 mol%) in EtOH (12 mL) was similarly purged with N₂ gas for 10 min and then with acetylene gas for 30 min. The solution of diyne 2a was then slowly added to the solution of Wilkinson’s catalyst at 60 °C over 4 h by using a syringe pump. The mixture was stirred overnight then filtered through Celite and concentrated in vacuo. The residue was purified by column chromatography [silica gel, EtOAc–hexane (45:55)] to give a yellow solid; yield: 407 mg (75%); mp 131–132 °C. FTIR (nujol): 3439 cm^–1. ¹H NMR (400 MHz, CDCl₃): δ = 7.45 (d, J = 6.8 Hz, 1 H), 7.37–7.28 (m, 3 H), 7.05–7.01 (m, 2 H), 5.31 (q, J = 5.9 Hz, 1 H), 3.93 (s, 3 H), 3.22 (s, 3 H), 3.14–3.06 (m, 1 H), 2.90–2.83 (m, 1 H), 2.52–2.44 (m, 1 H), 1.99–1.90 (m, 1 H). ¹³C NMR (100 MHz, CDCl₃): δ = 151.3, 146.2, 141.3, 141.1, 137.7, 137.6, 128.7, 127.7, 124.5, 123.9, 121.4, 113.5, 76.6, 56.2, 38.5, 36.3, 29.9. MS (ESI): m/z = 335.18 [M + H]⁺. HRMS (ESI): m/z [M + H]⁺ calcd for C₁₇H₁₉O₅S: 335.0953; found: 335.1602, 335.2099.
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• 9 For a comparison of all of the NMR data, see the Supporting Information.
• 10 CCDC 1913019 contains the supplementary crystallographic data for compound 1. The data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/getstructures.
• 11 Maier ME. Nat. Prod. Rep. 2009; 26: 1105
• 12 Attempts to contact the corresponding author of Ref. 1 met with no reply.