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Synlett 2005(2): 289-293  
DOI: 10.1055/s-2004-837213
LETTER
© Georg Thieme Verlag Stuttgart · New York

Unexpected cis-Selectivity in (Sylvestre) Julia Olefinations with Bu3Sn-Containing Allyl Benzothiazolyl Sulfones: Stereoselective Synthesis of 1,3-Butadienyl- and 1,3,5-Hexatrienylstannanes

Achim Sorg, Reinhard Brückner*
Institut für Organische Chemie und Biochemie, Albert-Ludwigs-Universität Freiburg, Albertstr. 21, 79104 Freiburg, Germany
Fax: +49(761)2036100; e-Mail: reinhard.brueckner@organik.chemie.uni-freiburg.de;
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Publikationsverlauf

Received 28 October 2004
Publikationsdatum:
17. Dezember 2004 (online)

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Abstract

Bu3Sn-substituted benzothiazolyl sulfones 1c, 1d, and 1f were subjected to Julia olefination reactions with a variety of aldehydes. cis-Selectivities up to 97:3 were obtained by using KHMDS as base in THF.

Key words

alkenylstannanes - dienes - Julia-Lythgoe olefination - stereoselectivity - trienes

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3,8-Dimethyl-1,10-bis(tributylstannyl)-1,3,5,7,9-decapentaene as a 94:6 mixture of cis-3 and trans-3: At
-78 °C KHMDS (1.0 M in THF, 0.26 mL, 0.26 mmol, 1.12 equiv) was added to a solution of sulfone 1f (147.3 mg, 0.259 mmol, 1.12 equiv) and aldehyde 2 (89.0 mg, 0.231 mmol, 1.00 equiv) in THF (1.5 mL), resulting in a purple solution. This solution was warmed to r.t. over a period of 2 h. Pentane (4 mL) and brine (2 mL) were added. The aqueous phase was extracted with pentane (2 × 2 mL) and the combined organic extracts were washed with brine (2 mL). After drying with Na2SO4 the solvent was removed in vacuo. Flash chromatography [Al2O3 (deactivated with 3% H2O), cyclohexane: Et3N = 200:2] afforded the title compound (142.2 mg, 63%; ref. [11] : 83%) as a 94:6 mixture of cis-3 and trans-3 as a yellow oil. IR (film): n = 2955, 2925, 2870, 2855, 1560, 1465, 1455, 1375, 1070, 1005, 980, 960, 880, 875, 865, 760, 690, 665, 595 cm-1. 1H NMR (499.9 MHz, C6HD5 as internal standard in C6D6): δ = ca. 0.91-1.09 (m, 6 × SnCH 2 CH2CH2CH3), in part superimposed by 0.93 (t, J vic = 7.3 Hz, 6 × SnCH2CH2CH2CH 3 ), 1.38 (tq, both J vic = 7.6 Hz, 6 × SnCH2CH2CH 2 CH3), 1.54-1.72 (m, 6 × SnCH2CH 2 CH2CH3), 1.87 (d, J allyl = 0.6 Hz, 3-CH3, 8-CH3), 6.44 (mc, 5-H, 6-H), 6.53 (d, J 1,2 and J 10,9 = 19.1 Hz, flanked by Sn isotope satellites as 2 interlocked d, 2 J ¹¹9 Sn,H = 69.8 Hz, 2 J ¹¹7 Sn,H = 66.3 Hz, 1-H, 10-H), 6.85 (br d, J 4,5 and J 7,6 = 8.2 Hz, 4-H, 7-H), 6.94 (d, J 2,1 and J 9,10 = 19.2 Hz, flanked by Sn isotope satellites as 2 interlocked d, 3 J ¹¹9 Sn,H = 64.9 Hz, 3 J ¹¹7 Sn,H = 62.1 Hz, 2-H, 9-H). 13C NMR (125.7 MHz, C6HD5 as internal standard in C6D6): δ = 9.89 (flanked by Sn isotope satellites as 2 d, 1 J ¹¹9 Sn,C-1 ′′ = 342.1 Hz, 1 J ¹¹7 Sn,C-1 ′′ = 327.0 Hz, SnCH2CH2CH2CH3), 12.01 (3-CH3, 8-CH3), 13.90 (SnCH2CH2CH2 CH 3 ), 27.69 (flanked by Sn isotope satellites as 1 d, 3 J ¹¹9 Sn,C-3 ′′ = 3 J ¹¹7 Sn,C-3 ′′ = 54.2 Hz, SnCH2CH2 CH2CH3), 29.58 (flanked by Sn isotope satellites as 1 d, 2 J ¹¹9 Sn,C-2 ′′ = 2 J ¹¹7 Sn,C-2 ′′ = 20.6 Hz, SnCH2 CH2CH2CH3), 126.63 (C-5, C-6), 126.93 (C-4, C-7), 128.93 (C-1, C-10), 137.95 (half intensity, C-3, C-8), 151.69 (flanked by Sn isotope satellites as 1 d, 2 J ¹¹9 Sn,C-2 = 2 J ¹¹7 Sn,C-2 and 2 J ¹¹9 Sn,C-9 = 2 J ¹¹7 Sn,C-9 = 10.9 Hz, C-2, C-9). The cis configuration of the C5=C6 double bond was proved by an edited HSQC experiment (‘1H-coupled short-range H,C-COSY’, 499.9/125.7 MHz, C6D6): The 13C signal at δ = 126.63 (C-5/C-6), split by 1 J C-5,5-H = 1 J C-6,6-H = 155.8 Hz, revealed the H,H coupling constants J 5,4 = J 5,6 and J 6,7 =
J 6,5 = 11.2 Hz. HRMS (EI, 70 eV): m/z = 681.26813 [M+ - Bu], which is 3.89 ppm more than calcd for C32H59Sn2 (m/z = 681.26548).

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Sorg, A. Dissertation; Universität Freiburg, 2004.

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All new compounds gave satisfactory 1H NMR and 13C NMR spectra and provided correct combustion analyses or high resolution mass spectra.

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Cis:trans ratios up to >99:1 for (Sylvestre) Julia olefinations of pentanal or octanal with (γ-butylpropargyl) benzothiazolyl sulfone, LiBr, and LDA in THF: see ref.3c

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After terminating the present study, we learned that Professor de Lera and associates observed cis-selective (Sylvestre) Julia olefinations, too, starting from a series of polyenyl benzothiazolyl sulfones including sulfone 1f. In their study, these authors (Vaz, B.; Alvarez, R.; Souto, J. A.; de Lera, A. R. Synlett 2005, following paper) had independently revised the stereochemical outcome of their olefination 1f + 2 → 3 in favor of the selectivity depicted in Scheme [1] .