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Synlett 2011(3): 365-368  
DOI: 10.1055/s-0030-1259505
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Regioselective Ring-Opening Reaction of Unsymmetrical 2,3-Diaryl Epoxides via Catalytic Hydrogenolysis with Pd(0)EnCatTM

Tetsutaro Kimachi*, Hiroyo Nagata, Yusuke Kobayashi, Kaori Takahashi, Eri Torii, Motoharu Ju-ichi
School of Pharmaceutical Sciences, Mukogawa Women’s University, 11-68 Koshienkyubancho, Nishinomiya 663-8179, Hyogo, Japan
Fax: +81(798)459952; e-Mail: tkimachi@mukogawa-u.ac.jp;
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Publication History

Received 28 October 2010
Publication Date:
25 January 2011 (online)

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Abstract

A series of unsymmetrical 2,3-diaryl epoxides were hydrogenated under transfer-hydrogenation conditions using the polyurea-encapsulated palladium catalyst [Pd(0)EnCatTM]. The position of the cleaved C-O bond was determined by ¹H NMR analysis of the ring-opened products derived from the epoxide, in which one of the two benzylic methyne protons is deuterated. The ratio of ring-opened products of the unsymmetrically substituted 2,3-diaryl epoxides was affected by the degree of the steric bulkiness on the ­aromatic ring.

Key words

reductive ring-opening reaction - polyurea-encapsul­ated palladium catalyst [Pd(0)EnCatTM] - 2,3-diary epoxide - Darzens reaction

    References and Notes

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7

Typical Procedure for the Reductive Ring-Opening Reaction of the Epoxides 4-11 and Deuterated Epoxides (4- d -11- d )
Pd(0) catalyst [Pd(0)EnCatTM, 50 mg, 0.02 mmol] was added to a solution of the epoxide (0.38 mmol) in EtOAc (0.75 mL) at r.t. under argon atmosphere. The mixture was cooled to 0 ˚C, Et3N (0.28 mL, 4 mmol) and formic acid (0.07 mL, 4 mmoL) were added. After 5 h stirring at r.t., the mixture was worked up as follows. The resulting Pd(0) was filtered off, then filtrate was concentrated under reduced pressure. The remaining residue was purified by flash chromatography to afford the product.
¹ H NMR Spectra of the Ring-Opened Products 12-21
Product 12: ¹H NMR (400 MHz, CDCl3): δ = 1.65 (s, 1 H), 2.35 (s, 3 H), 2.91-3.06 (m, 2 H), 4.85-4.89 (m, 1 H), 7.10-7.36 (m, 9 H).
Product 13: ¹H NMR (400 MHz, CDCl3): δ = 1.90 (s, 1 H), 3.00 (m, 2 H), 3.80 (s, 3 H), 4.84 (dd, 1 H, J = 5.9, 7.3 Hz), 6.85-6.89 (m, 2 H), 7.16-7.34 (m, 7 H).
Product 14: ¹H NMR (500 MHz, CDCl3): δ = 1.11 (m, 3 H), 1.22 (m, 3 H), 2.97 (dd, 1 H, J = 8.2, 13.7 Hz), 3.03 (dd, 1 H, J = 5.0, 13.7 Hz), 3.25 (m, 2 H), 3.53 (m, 2 H), 4.91 (dd, 1 H, J = 5.0, 8.2 Hz), 7.16-7.36 (m, 9 H).
Product 15: ¹H NMR (400 MHz, CDCl3): δ = 1.60 (s, 9 H), 2.97 (dd, 1 H, J = 8.4, 13.9 Hz), 3.04 (dd, 1 H, J = 4.8, 13.9 Hz), 4.95 (m, 1 H), 7.16-7.18 (m, 2 H), 7.22-7.32 (m, 3 H), 7.38 (d, 2 H, J = 8.4 Hz), 7.95 (d, 2 H, J = 8.4 Hz).
Product 16: ¹H NMR (400 MHz, CDCl3): δ = 1.32 (s, 9 H), 1.89 (s, 1 H), 2.97 (dd, 1 H, J = 10.2, 13.5 Hz), 3.04 (dd, 1 H, J = 4.4, 13.5 Hz), 4.86 (m, 1 H), 7.20-7.30 (m, 5 H), 7.31 (d, 2 H, J = 8.4 Hz), 7.37 (d, 2 H, J = 8.4 Hz).
Product 17: ¹H NMR (400 MHz, CDCl3): δ = 2.1 (d, 1 H, J = 3.0 Hz), 2.94 (dd, 1 H, J = 8.4, 13.5 Hz), 3.03 (dd, 1 H, J = 4.8, 13.5 Hz), 4.95 (m, 1 H), 7.14-7.36 (m, 5 H), 7.43 (d, 2 H, J = 8.0 Hz), 7.61 (d, 2 H, J = 8.0 Hz).
Product 18: ¹H NMR (400 MHz, CDCl3): δ = 1.98 (m, 1 H), 3.05 (m, 1 H), 3.13 (m, 1 H), 4.90 (m, 1 H), 7.24-7.36 (m, 5 H), 7.27 (d, 2 H, J = 8.3 Hz), 7.54 (d, 2 H, J = 8.3 Hz).
Product 19: ¹H NMR (500 MHz, CDCl3): δ = 3.07 (d, 2 H, J = 6.4 Hz), 5.00 (t, 1 H, J = 6.4 Hz), 7.27 (d, 2 H, J = 8.2 Hz), 7.42 (d, 2 H, J = 8.2 Hz), 7.57 (d, 2 H, J = 8.2 Hz), 7.60 (d, 2 H, J = 8.2 Hz).
Product 20: ¹H NMR (400 MHz, CDCl3): δ = 2.89 (dd, 1 H, J = 8.4, 13.9 Hz), 2.99 (dd, 1 H, J = 4.8, 13.5 Hz), 3.79 (s, 3 H), 4.91 (m, 1 H), 6.84 (d, 2 H, J = 8.4 Hz), 7.08 (d, 2 H, J = 8.4 Hz), 7.45 (d, 2 H, J = 8.1 Hz), 7.59 (d, 2 H, J = 8.1 Hz).
Product 21: ¹H NMR (400 MHz, CDCl3): δ = 3.04-3.08 (m, 2 H), 3.81 (s, 3 H), 4.86 (m, 1 H), 6.87 (d, 2 H, J = 8.8 Hz), 7.22-7.28 (m, 4 H), 7.52 (d, 2 H, J = 8.1 Hz).
¹ H NMR Spectra of Deuterated Ring-Opened Products 12- d -21- d
Product 12-d: ¹H NMR (400 MHz, CDCl3): δ = 2.34 (s, 3 H), 2.94-3.01 (m, 1 H), 4.83-4.85 (m, 1 H), 7.06-7.36 (m, 10 H).
Product 13-d: ¹H NMR (400 MHz, CDCl3): δ = 3.00 (s, 2 H), 3.80 (s, 3 H), 6.87 (d, 2 H, J = 8.8 Hz), 7.26 (d, 2 H, J = 8.8 Hz), 7.16-7.30 (m, 5 H).
Product 14-d: ¹H NMR (400 MHz, CDCl3): δ = 1.14 (m, 3 H), 1.22 (m, 3 H), 2.05 (s, 1 H), 3.02 (d, 1 H, J = 4.4 Hz), 3.27 (m, 2 H), 3.53 (m, 2 H), 4.92 (d, 1 H, J = 4.4 Hz), 7.17-7.38 (m, 9 H).
Product 15-d: ¹H NMR (400 MHz, CDCl3): δ = 1.60 (s, 9 H), 1.99 (d, 1 H, J = 3.2 Hz), 3.02 (d, 1 H, J = 4.6 Hz), 4.95 (m, 1 H), 7.15-7.18 (m, 2 H), 7.22-7.32 (m, 3 H), 7.38 (d, 2 H, J = 8.2 Hz), 7.95 (d, 2 H, J = 8.2 Hz).
Product 16-d: ¹H NMR (400 MHz, CDCl3): δ = 1.31 (s, 9 H), 1.89 (s, 1 H), 3.04 (d, 1 H, J = 4.4 Hz), 4.86 (d, 1 H, J = 4.4 Hz), 7.20-7.30 (m, 5 H), 7.31 (d, 2 H, J = 8.4 Hz), 7.37 (d, 2 H, J = 8.4 Hz).
Product 17-d: ¹H NMR (400 MHz, CDCl3): δ = 2.07 (d, 1 H, J = 3.2 Hz), 3.01 (m, 1 H), 4.95 (m, 1 H), 7.27-7.40 (m, 5 H), 7.43 (d, 2 H, J = 8.3 Hz), 7.62 (d, 2 H, J = 8.3 Hz).
Product 18-d: ¹H NMR (400 MHz, CDCl3): δ = 2.00 (br s, 1 H), 3.05 (m, 1 H), 3.10 (m, 1 H), 7.37 (m, 5 H), 7.30 (d, 2 H, J = 8.3 Hz), 7.55 (d, 2 H, J = 8.3 Hz).
Product 19-d: ¹H NMR (400 MHz, CDCl3): δ = 1.96 (s, 1 H), 3.07 (s, 2 H), 7.27 (d, 2 H, J = 8.1 Hz), 7.42 (d, 2 H, J = 8.1 Hz), 7.56-7.65 (m, 4 H).
Product 20-d: ¹H NMR (400 MHz, CDCl3): δ = 1.98 (d, 1 H, J = 3.3 Hz), 2.98 (m, 1 H), 3.79 (s, 3 H), 4.91 (s, 1 H), 6.85 (d, 2 H, J = 8.1 Hz), 7.08 (d, 2 H, J = 8.1 Hz), 7.45 (d, 2 H, J = 8.4 Hz), 7.59 (d, 2 H, J = 8.4 Hz).
Product 21-d: ¹H NMR (400 MHz, CDCl3): δ = 1.81 (s, 1 H), 3.06 (dd, 2 H, J = 13.5, 23.8 Hz), 3.81 (s, 3 H), 6.88 (d, 2 H, J = 8.8 Hz), 7.24 (d, 2 H, J = 8.8 Hz), 7.27 (d, 2 H, J = 8.1 Hz), 7.53 (d, 2 H, J = 8.1 Hz).