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Synlett 2002(1): 0043-0044
DOI: 10.1055/s-2002-19323
LETTER
© Georg Thieme Verlag Stuttgart · New York

Highly Enantioselective Catalytic Ketone Allylation with Sn(CH2CH=CH2)4/RSn(CH2CH=CH2)3 Mixtures (R = Et, Bu)

Anthony Cunningham, Simon Woodward*
School of Chemistry, The University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom
Fax: +44(115)9513564; e-Mail: simon.woodward@nottingham.ac.uk;
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Publication History

Received 19 September 2001
Publication Date:
01 February 2007 (online)

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Highly Enantioselective Catalytic Ketone Allylation with Sn(CH2CH=CH2)4/RSn(CH2CH=CH2)3 Mixtures (R = Et, Bu) Synlett 2004; 2004(05): 0914-0914
DOI: 10.1055/s-2004-820040

Abstract

In the presence of the monothiobinaphthol (MTB) ligand aryl ketones are allylated by mixtures of Sn(CH2CH=CH2)4/RSn(CH2CH=CH2)3 (R = Et, Bu) in high e.e. The presence of water suppresses racemic background allylation.

Key words

tin - asymmetric catalysis - ketones - allylation - thiols

    References

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10

Other EtnSn(CH2CH=CH2)4-n, n = 2-4 species are also present as very minor contaminants in these preparations. Control reactions using d5-EtBr confirm that the ethyl group arises from the EtBr used for magnesium activation in ref. 9. Fresh (silver-coloured) as opposed to aged (>2 years, black-coloured) magnesium leads only to pure Sn(CH2CH=CH2)4. Electron microscopy in conjunction with EDS studies reveal that the surface of aged magnesium has an appreciable oxygen content (presumably MgO) and it appears to be this that favours production of EtMgBr over CH2=CHCH2MgCl.

14

Experimental Procedure: All operations were performed under argon; toluene was distilled from sodium. A toluene solution of MTB 2 (24 mg, 0.08 mmol in 1.0 mL) was treated with a mixture of Sn(CH2CH=CH2)4/SnR(CH2CH=CH2)3 (0.7:0.3 mol fraction mix, 0.46 mmol total Sn content, R = Et, Bu). For the ‘dry’ catalyst this mixture (R = Et) was heated directly for 2 h at 52 °C. For the ‘wet’ catalyst water (3 µL, 0.16 mmol) was added to the mixture (R = Bu) prior to the heating period. The mixtures were cooled to ambient temperature, the ketone 1 (or 4) (0.4 mmol) added and the mixture stirred whilst its composition was monitored by GC, HPLC, or 1H/119Sn NMR spectroscopy. Flash chromatography afforded the known alcohols 3 (or 5) as essentially single products. Enantioselectivities were determined by GC (CYCLODEX-B for 3c, oktakis(6-O-methyl-2,3-di-O-pentyl)-γ-cyclodextrin for 3a, 3b, 3e, 3f, 5) or HPLC (Chiralcel AD for 3d, Chiralcel OD for 3g).