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Synthesis 2007(6): 883-892  
DOI: 10.1055/s-2007-965928
PAPER
© Georg Thieme Verlag Stuttgart · New York

Chain-Elongation of Sugar Aldehydes by Asymmetric Homoaldol Reaction: Introduction of a Functionalized 3-Methyl-Substituted Three-Carbon Unit

Sabine Kollmann, Roland Fröhlich, Dieter Hoppe*
Westfälische Wilhelms-Universität Münster, Organisch-Chemisches Institut, Corrensstraße 40, 48149 Münster, Germany
Fax: +49(251)8336531; e-Mail: dhoppe@uni-muenster.de ;
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Publication History

Received 17 October 2006
Publication Date:
08 February 2007 (online)

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Abstract

O-Protected aldehydo-sugars reacted with α-titanated crotyl N,N-diisopropylcarbamate to furnish chain-elongated alk-1-enyl carbamates. These were further functionalized by epoxidation of the double bond and subsequent methanolysis to form methyl 3-C-methyl-3-deoxy-furanosides. Mukaiyama-type addition of benzaldehyde led to tetrasubstituted tetrahydrofurans. All reactions proceeded with high diastereoselectivities and allow for a broad application.

Key words

homoaldol reaction - epoxides - (-)-sparteine-mediated metalation - stereoselective synthesis - branched carbohydrates

1

X-ray crystal structure analysis.

21

X-ray crystal structure analysis for 16d: Formula C22H39NO7, M = 429.54, colorless crystal 0.40 × 0.30 × 0.30 mm, a = 10.239 (1), b = 12.544 (1), c = 10.305 (1) Å, β = 115.42 (1), V = 1195.4 (2) Å3, ρcalc = 1.193 g cm-3, µ = 0.088 mm-1, empirical absorption correction (0.966 ≤ T ≤ 0.974), Z = 2, monoclinic, space group P21 (No. 4), λ = 0.71073 Å, T = 198 K, ω and φ scans, 11178 reflections collected (± h, ± k, ± l), [(sin θ)/λ] = 0.67 Å-1, 5221 independent (R int = 0.063) and 3783 observed reflections [I ≥ 2 σ (I)], 282 refined parameters, R = 0.045, wR 2 = 0.104, Flack parameter -0.1 (8), max. residual electron density 0.19 (-0.17) e Å-3, hydrogen atoms calculated and refined as riding atoms.

25

We isolated and characterized this type of intermediate previously. [8]

26

Carbohydrate numberings which matches with those of the open-chain precursor 16.

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X-ray crystal structure analysis for 26c: Formula C23H30O7, M = 418.47, colorless crystal 0.30 × 0.20 × 0.15 mm, a = 10.573 (1), b = 10.872 (1), c = 19723 (1) Å, V = 2267.2 (3) Å3, ρcalc = 1.226 g cm-3, µ = 0.744 mm-1, empirical absorption correction (0.808 ≤ T ≤ 0.897), Z = 4, orthorhombic, space group P212121 (No. 19), λ = 1.54178 Å, T = 293 K, ω and φ scans, 22050 reflections collected (± h, ± k, ± l), [(sin θ)/λ] = 0.60 Å-1, 4065 independent (R int = 0.039) and 3861 observed reflections [I ≥ 2 σ (I)], 276 refined parameters, R = 0.033, wR 2 = 0.089, Flack parameter 0.07 (15), max. residual electron density 0.17 (-0.12) e Å-3, hydrogen atoms calculated and refined as riding atoms.

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Data sets were collected with Nonius KappaCCD diffractometers, in case of Mo-radiation equipped with a rotating anode generator. Programs used: data collection COLLECT, [32] data reduction Denzo-SMN, [33] absorption correction SORTAV [34] and Denzo, [35] structure solution SHELXS-97, [36] structure refinement SHELXL-97, [37] and graphics SCHAKAL. [38] CCDC 621679 & 621680 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge at www.ccdc.cam.ac.uk/conts/retrieving.html [or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033, E-mail: deposit@ccdc.cam.ac.uk].