An Efficient Synthesis of 4.4-Dephenylcyclopentene

References

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• two-step synthesis: reference 3
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• Treatement of 4 with Na/liq.NH3 or Na/liq.NH3/ClSiMe3 according to the procedure described respectively by N. L. Allinger, (Org. Syn., 1963, 4, 840) and J. J. Bloom field and coll. (Org. Syn., 1977, 57, 1) did not give the expected acyloin condensation products
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• The assignment of structures of 7 and 8 was based on their chemical transformation: trans-diol 7 was directly converted to the epoxide 9 (see scheme) and cis-diol 8 to the corresponding 2-methoxy-1,3-dioxolane 13 (see note 10). Structural assignments were confirmed by 13C-NMR (DMSO-d6, 75MHz): the cis-isomer 8 possesses two non-equivalent phenyl groups whereas the trans-isomer 7 does not
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• 4,4-Diphenylcyclopentene 1 can also be synthesized from cis-diol 8 : thus treatment of 8 with trimethyl orthoformate in the presence of pyridinium p-toluenesulfonate gave the corresponding 2-methoxy-1,3-dioxolane 13 in 70%. Conversion of 13 to the desired 4,4-diphenylcyclopentene 1 in 56% yield was achieved by refluxing in acetic anhydride
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• We also synthesized cis-diol 8 in low yields (5–10%) using the following procedures: The reduction of 4 by diisobutylaluminum hydride (see: M. J.Kukla and H. J.Breslin, J.Org.Chem., 1987, 52, 5046) gave 3,3-diphenylglutaraldehyde which was submitted, without purification, to intramolecular reductive cyclization using either Mg(Hg)-TiCl4 (see: E. J.Corey, R. L. Danheiser, S. Chandrasekaran, J. Org. Chem., 1976, 41 (2), 260) or Sml2 (see: J. L. Namy, J. Souppe, H. B. Kagan, Tetrahedron Letters, 1983, 24 (8), 765) to give 8. The low yielding synthesis of diol 8 precludes its utilization as a starting material for 1 using the scheme depicted in the reference 10
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• Kugelrohr distillation of this brown-yellow oil allows the isolation of the intermediate l,2-bis(trimethylsilyloxy)-4,4-diphenylcyclopentene 14 as a pale yellow oil.
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• 1H-NMR (CDCl3, 200MHz) δ: 0.15 (s, 18H, 2 × SiMe3); 3.0 (s, 4H, 2 × CH2); 7.10–7.35 (m, 10H, 2 × C6H5)., MS (El) m/z (%): 396 (15, M+-), 307 (7, -OSiMe3), 73 (100)., IR(CHCl3) ν max: 3080 and 3060 (aromatic CH); 2960 (CH3); 2860 (CH2 and CH3); 1600, 1580, 1490 and 1445 (aromatic ring); 1225 (CO and CH3); 880 and 850 cm−1 (CH3)
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