New Observations in Organozinc Chemistry: Control of Relative Stereo­chemistry in Reactions of Silicon Substituted Alkenylzinc Reagents

E. M. E. Viseux; P. J. Parsons; J. B. J. Pavey

doi:10.1055/s-2003-38727

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Synlett 2003(6): 0861-0863
DOI: 10.1055/s-2003-38727

LETTER

New Observations in Organozinc Chemistry: Control of Relative Stereochemistry in Reactions of Silicon Substituted Alkenylzinc Reagents

E. M. E. Viseux^a, P. J. Parsons*^a, J. B. J. Pavey^b
^a The Chemical Laboratories, School of Chemistry, Physics & Environmental Science, University of Sussex, Falmer, Brighton, East Sussex BN1 9QJ, UK
Fax: +44(1273)677196; e-Mail: P.J.Parsons@sussex.ac.uk;
^b AstraZeneca R&D Charnwood, Process R&D, Bakewell Road, Loughborough, Leics LE11 5RH, UK

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Publication History

Received 17 March 2003
Publication Date:
17 April 2003 (online)

Abstract
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Abstract

Reagents have been synthesised that behave as both Lewis acids and nucleophiles. Reaction of these reagents with electrophiles has led to the finding that diastereoselectivity is observed upon addition to aldehydes. An ordered transition state to account for the observed stereochemistry is proposed herein.

Key words

organozinc - organosilicon - diastereocontrol - silicon rearrangement - diastereoselectivity

References

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2

Typical Procedure for the Rearrangement: The organozinc reagent 1 was canulated into a solution of 2-(methoxymethoxy)-pentanal 2 (0.734 g, 5.02 mmol, 1 equiv) in Et₂O (10 mL) over 15 min at -20 °C. The mixture was then allowed to warm to r.t. and stirred a further 10 h, before aq HCl (10 mL, 1 M) was added. The resulting phases were separated, and the aqueous layer extracted with Et₂O (3 ¥ 5 mL). The combined organic layers were washed with brine (10 mL), dried over MgSO₄, filtered and concentrated under reduced pressure. The resulting yellow oil was subjected to flash chromatography (Et₂O-petroleum ether, 10:90) to yield 5-methoxymethoxy-2-trimethylsilanyl-oct-1-en-4-ol (4a) as a clear colourless oil (0.914 g, 80%).
¹H NMR (300 MHz, CDCl₃): δ = 5.67-5.70 (1 H, m, CH ₂ alkene), 5.47 (1 H, d, J _gem = 3 Hz, CH ₂ alkene), 4.68-4.71 (2 H, m, AB system, CH ₂O), 3.61-3.71 (1 H, m, CHOH), 3.4 (3 H, s, CH ₃O), 2.15-2.47 (3 H, m, CHO and CH ₂ allylic), 1.19-1.7 (4 H, m, CH ₂), 0.92 (3 H, t, J = 7 Hz, CH ₃), 0.11 (9 H, s, CH ₃Si).
¹³C NMR (75.432 MHz, CDCl₃): δ = 149.02 (C), 127.31 (CH₂), 96.79 (CH₂O), 81.59 (CHO), 70.79 (CHO), 55.81 (CH₃O), 40.334 (CH₂ allylic), 33.06 (CH₂), 18.65 (CH₂), 14.18 (CH₃), -1.35 (CH₃Si).
IR (thin film): 3478, 2956, 1247, 1099, 1034, 921, 834, 757 cm^-1.