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Synlett 2008(15): 2271-2274  
DOI: 10.1055/s-2008-1078271
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

A Catalytic Asymmetric Fujiwara-Moritani Cyclization

Julia A. Schiffner, Axel B. Machotta, Martin Oestreich*
Organisch-Chemisches Institut, Westfälische Wilhelms-Universität, Corrensstraße 40, 48149 Münster, Germany
Fax: +49(251)8336501; e-Mail: martin.oestreich@uni-muenster.de;
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Publikationsverlauf

Received 15 May 2008
Publikationsdatum:
21. August 2008 (online)

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Abstract

An enantioselective intramolecular Fujiwara-Moritani reaction involving direct C-H functionalization using modified PyOX ligands is reported for the first time. Screening of several ligand-oxidant combinations eventually produced a stereogenic quaternary carbon with promising enantiocontrol (54% ee) and in good chemical yield (71%).

Key words

asymmetric catalysis - cyclizations - Fujiwara-Moritani reaction - oxidative Heck reaction - palladium

    References and Notes

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  • 23a

    Analytical Data for ( Z )- or ( E )-1-Methyl-3-(3-methylpent-3-enyl) indole [( Z )-1 or ( E )-1] ¹4a
    (Z)-1 (Z/E > 99:1): ¹H NMR (300 MHz, CDCl3): δ = 1.62 (d, J = 6.7 Hz, 3 H), 1.82-1.86 (m, 3 H), 2.48 (br t, J = 8.4 Hz, 2 H), 2.83-2.91 (m, 2 H), 3.78 (s, 3 H), 5.32 (q, J = 6.7 Hz, 1 H), 6.90 (s, 1 H), 7.13-7.20 (m, 1 H), 7.24-7.31 (m, 1 H), 7.31-7.36 (m, 1 H), 7.68 (ddd, J = 7.8, 1.7, 0.9 Hz, 1 H) ppm. ¹³C NMR (75 MHz, CDCl3): δ = 13.3, 23.4, 23.5, 32.5, 32.5, 109.1, 115.3, 118.5, 118.9, 119.2, 121.4, 125.8, 127.9, 136.1, 137.0 ppm.
    (E)-1 (E:Z > 99:1): ¹H NMR (300 MHz, CDCl3): δ = 1.67 (dq, J = 6.7, 1.0 Hz, 3 H), 1.77 (m, 3 H), 2.39-2.49 (m, 2 H), 2.87-2.94 (m, 2 H), 3.78 (s, 3 H), 5.37 (qq, J = 6.8, 1.3 Hz, 1 H), 6.88 (s, 1 H), 7.16 (ddd, J = 8.0, 6.8, 1.3 Hz, 1 H), 7.27 (ddd, J = 8.2, 6.8, 1.2 Hz, 1 H), 7.33 (ddd, J = 8.2, 1.1, 0.9 Hz, 1 H), 7.66 (ddd, J = 7.8, 0.9 Hz, 1 H) ppm. ¹³C NMR (75 MHz, CDCl3): δ = 13.4, 15.8, 24.0, 32.5, 40.5, 109.0, 115.3, 118.4, 118.4, 119.0, 121.3, 125.8, 127.9, 135.9, 136.9 ppm.

  • 23b

    Analytical Data for (-)-3,4-Dimethyl-3-vinyl-1,2,3,4-tetrahydrocyclopenta[ b ]indole [(-)-2]
    [α]D ²0 -17.7 (c 0.565, CHCl3) for 44% ee (Table  [³] , entry 2). HPLC (Daicel Chiralcel IB column using n-heptane at 15 ˚C): t R = 13.9 min (minor enantiomer) and 16.1 min (major enantiomer). IR (film): 3052 (m), 2926 (s), 2854 (s), 1465 (s) cm-¹. ¹H NMR (300 MHz, CDCl3): δ = 1.50 (s, 3 H), 2.36 (ddd, J = 13.0, 7.1, 6.1 Hz, 1 H), 2.47-2.58 (m, 1 H), 2.83 (m, 2 H), 3.64 (s, 3 H), 4.98 (dd, J = 17.4, 1.3 Hz, 1 H), 5.06 (dd, J = 10.5, 1.2 Hz, 1 H), 6.09 (dd, J = 17.4, 10.5 Hz, 1 H), 7.09 (ddd, J = 7.5, 7.1 Hz, 1.3 Hz, 1 H), 7.16 (ddd, J = 8.2, 7.0, 1.4 Hz, 1 H), 7.26 (ddd, J = 8.1, 0.9, 0.8 Hz, 1 H), 7.47 (ddd, J = 7.6, 1.3, 0.7 Hz, 1 H) ppm. ¹³C NMR (75 MHz, CDCl3): δ = 22.5, 23.7, 30.0, 46.0, 46.3, 109.3, 111.8, 117.3, 118.8, 119.0, 120.2, 123.9, 141.6, 145.1, 148.7 ppm. ESI-HRMS: m/z calcd for C15H17NNa: 234.1259; found: 234.1253. Anal. Calcd for C15H17N: C, 85.26; H, 8.11; N, 6.63. Found: C, 84.97; H, 8.20; N, 6.54.

21

General Procedure for Fujiwara-Moritani Cyclization A flame-dried reaction vessel equipped with a magnetic stir bar is charged with Pd(OAc)2 (10 mol%) as well as the indicated ligand L2-8 (30 mol%) and subsequently evacuated and then backfilled with O2 if used as oxidant (three cycles). Otherwise, a solution of the indole and tert-amyl alcohol (0.125 M) and AcOH (0.25 mL per mL of tert-amyl alcohol) are consecutively added. The reaction mixture is maintained at r.t. until a homogeneous tawny solution forms. Then, the oxidant (1.0 equiv), PhCO3 t-Bu or 1,4-benzoquinone, is added, and the resulting reaction mixture is heated at 80 ˚C for 15 h (under O2 atmosphere with O2 as the oxidant). After cooling to r.t., the reaction mixture is diluted with MTBE and poured into H2O. The organic layer is separated and washed with sat. aq NaHCO3 and brine. The aqueous phase is extracted with MTBE and the combined organic extracts are dried over Na2SO4. The solvents are evaporated under reduced pressure, and the residue is purified by flash column chromatography on SiO2 using cyclohexane-MTBE solvent mixtures.