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DOI: 10.1055/s-2001-16083
Regioselective Superacid-Catalyzed Electrocyclization of Diphenylmethyl Cations to Fluorenes, Phenanthrols and Benzofurans
Publication History
Publication Date:
23 September 2004 (online)
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Abstract
Cationic electrocyclization of α-benzoyldiphenylmethanols in the presence of superacid provides fluorenes, phenanthrols and benzofurans in good to moderate yields. A single substitution leads to regioselective cationic electrocyclizations.
Key words
carbocations - electrocyclizations - regioselectivity - superacid - diphenylmethyl cations
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1a
Creary X. Chem. Rev. 1991, 91: 1625 -
1b
Creary X.Hopkinson AC.Lee-Ruff E. Advances in Carbocation Chemistry Vol. 1:Creary X. JAI Press; Greenwich, CT: 1989. p.45 -
1c
Gassman PG.Tidwell TT. Acc. Chem. Res. 1983, 16: 279 -
1d
Tidwell TT. Angew. Chem., Int. Ed. Engl. 1984, 23: 20 -
2a
Dao LH.Maleki M.Hopkinson AC.Lee-Ruff E. J. Am. Chem. Soc. 1986, 108: 5237 -
2b
Hopkinson AC.Lee-Ruff E.Maleki M. Synthesis 1986, 366 - 3
Johnston LJ.Kwong P.Shelemay A.Lee-Ruff E. J. Am. Chem. Soc. 1993, 115: 1664 - 4
Takeuchi K.Kitagawa T.Okamato K. J. Chem. Soc., Chem. Commun. 1983, 7 - 5 Photochemical cyclizations of methoxy-substituted benzoin esters (e. g., 4"-methoxybenzoin acetate) to give benzofurans (2-phenyl-6-methoxybenzofuran) was reported by
Sheehan JC.Wilson RM.Oxford AW. J. Am. Chem. Soc. 1971, 93: 7222 -
7a
Vorlander D.Pritzsche A. Ber. Dtsch. Chem. Ges. 1913, 46: 1793 -
7b
Britzrzycki A.Herbst C. Ber. Dtsch. Chem. Ges. 1903, 36: 145 -
7c
Dobeneck HV.Kiefer R. Liebigs Ann. Chem. 1965, 684: 115 -
7d
Arnold RT.Parham WE.Dodson RM. J. Am. Chem. Soc. 1949, 71: 2439 -
7e
Hopkinson AC.Khazanie PG.Dao LH. J. Chem. Soc., Perkin Trans. 2 1979, 1395 -
7f
Delacre M. Bull. Soc. Chim. Fr. 1918, 23: 229 -
8a
Ohwada T.Shudo K. J. Am. Chem. Soc. 1988, 110: 1862 -
8b
Ohwada T.Shudo K. J. Org. Chem. 1989, 54: 5227 - 9
Ohwada T.Suzuki T.Shudo K. J. Am. Chem. Soc. 1998, 120: 4629 - 10
Hopkinson AC.Dao LH.Duperrouzel P.Maleki M.Lee-Ruff E. J. Chem. Soc., Chem. Commun. 1983, 727 - 11
Maleki M.Hopkinson AC.Lee-Ruff E. Tetrahedron Lett. 1983, 24: 4911 -
12a
Olah GA.Wu A.-H. J. Org. Chem. 1991, 56: 2531 -
12b For a review of superelectrophiles, see:
Olah GA. Angew. Chem., Int. Ed. Engl. 1993, 32: 767 -
12c See also:
Olah GA.Klumpp DA.Nlyer G.Wang Q. Synthesis 1996, 321 -
13a
Krepski LR.Heilmann SM.Rasmussen JK. Tetrahedron Lett. 1983, 24: 4075 -
13b
Gassman PG.Talley JJ. Tetrahedron Lett. 1978, 3773 - 14
Johnson CD. Acc. Chem. Res. 1993, 26: 476 - 15
Chambers RD.Clark M. J. Chem. Soc., Perkin Trans. 1 1972, 2469
References
It was reported that α-acetyldiphenylmethanol (2b, R = CH3) and α-benzoyldiphenylmethanol (2d, R1 = R2 = H) cyclized in H2SO4-CHCl3 by an electrocyclization mechanism between the benzene ring and the carbonyl group, resulting in the formation of the corresponding benzofurans, [2] [10] although the formation of the fluorene derivative 4d from 2d has also been reported under similar conditions. [11]