Synlett 2004(2): 0231-0234  
DOI: 10.1055/s-2003-44977
LETTER
© Georg Thieme Verlag Stuttgart · New York

Allylation of Aldehydes, Aldimines and Ring Opening of Terminal Aromatic Epoxides by Scandium Triflate using Polyethylene Glycol (PEG) as an ­Efficient Recyclable Medium

Boyapati M. Choudary*, Karangula Jyothi, Sateesh Madhi, Mannepalli L. Kantam
Indian Institute of Chemical Technology, Hyderabad 500 007, India
Fax: +91(40)27160921; e-Mail: choudary@iict.res.in; bmchoudary@yahoo.com;
Further Information

Publication History

Received 23 June 2003
Publication Date:
04 December 2003 (online)

Abstract

Scandium triflate catalyzed allylation of a variety of aldehydes and aldimines using polyethylene glycol (PEG) as a recyclable reaction medium proceeds smoothly and affords corresponding homoallylic alcohols and amines in good yields. ­Furthermore this catalyst catalyzes total regioselective ring opening of terminal 1,2-epoxides to bishomoallylic alcohols in good yields. The PEG-scandium triflate catalyst system can be reused for a ­number of cycles without significant loss of activity.

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Typical Procedure for the Catalytic Allylation of Aldehydes: A mixture of p-nitrobenzaldehyde (1 mmol), allyltributylstannane (1.2 mmol), benzoic acid (1 mmol), PEG (2 g) and scandium triflate (5 mol%) was placed in a 25 mL round bottomed flask. The mixture was stirred at r.t. for 3 h (monitored by TLC). The reaction mixture was extracted with dry Et2O and the crude product was purified by column chromatography to obtain homoallylic alcohol in excellent yields. The products were characterized by 1H NMR data.
1H NMR (200 MHz, CDCl3): δ = 2.01 (d, 1 H, OH), 2.52 (m, 2 H, CH2), 4.80 (t, 1 H, CH), 5.14-5.20 (m, 2 H, 2 × vinyl), 5.82 (m, 1 H, vinyl), 7.50 (d, 2 H, aromatic), 8.20 (d, 2 H, aromatic).

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Typical Procedure for the One-Pot Catalytic Allylation of Aldimines: A mixture of p-nitrobenzaldehyde (1 mmol), p-nitroaniline (1 mmol) allyltributylstannane (1.2 mmol), benzoic acid (1 mmol), PEG (2 g) and scandium triflate 20 mol% was placed in a 25 mL round bottomed flask. The mixture was stirred at r.t. for 4 h (monitored by TLC). The reaction mixture was extracted with Et2O and the crude product was purified by column chromatography to obtain homoallylic amine in good yields. The products were characterized by 1H NMR data.
1H NMR (200 MHz, CDCl3): δ = 2.52 (m, 2 H, CH2), 4.60 (t, 1 H, CH), 5.20 (m, 2 H, 2 × vinyl), 5.85 (m, 1 H, vinyl), 7.55 (d, 4 H, aromatic), 8.25 (d, 4 H, aromatic).

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Typical Procedure for Regioselective Catalytic Allylation of Terminal Aromatic Epoxides: A mixture of styrene epoxide (1 mmol), allytributylstannane (1.2 mmol), and scandium triflate 5 mol%, PEG (2 g) was placed in a 25 mL round bottomed flask. The mixture was stirred at 55-60 °C for 24 h. The reaction mixture was cooled and was extracted by Et2O and the crude product was purified by column chromatography to obtain bishomoallylic alcohol in good yields. The products were characterized by 1H NMR data.
1H NMR (200 MHz, CDCl3): δ = 2.05-2.35 (m, 2 H), 2.70 (m, 2 H), 3.75 (m, 1 H), 5.01-5.10 (m, 2 H), 5.80 (m, 1 H), 7.12-7.30 (m, 5 H).

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Extraction with dry Et2O is essential for consistency in the activity of the reaction medium in the study of recycling.