Download PDF
Synlett 2003(7): 0967-0970
DOI: 10.1055/s-2003-39300
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

The Head-to-Head Reductive Coupling of Homoallylic Alcohols Promoted by Titanium(II)-Olefin Complexes

Vladimir E. Isakov, Oleg G. Kulinkovich*
Department of Organic Chemistry, Belarussian State University, 4, Skariny av., 220050 Minsk, Belarus
Fax: +375(172)265609; e-Mail: kulinkovich@bsu.by;
Further Information

Publication History

Received 25 February 2003
Publication Date:
20 May 2003 (online)

    Permissions and Reprints All articles of this category

Abstract

Reaction of homoallylic alcohols 1a-e with i-PrMgBr in the presence of Ti(i-PrO)4 leads to the unbranched saturated diols 2a-e as the main products in moderate to good yields. The head-to-head regioselectivity in reductive coupling of 4-penten-1-ol and 5-hexen-2-ol was also observed. Coupling of 2-methyl-5-hexen-2-ol, as well as unsaturated alcohols in which vinyl and hydroxyl groups are more distant from one another, proceeded with head-to-tail or tail-to-tail regioselectivity. It is supposed, that the unusual head-to-head regioselectivity in reductive coupling of homoallylic alcohols 1a-e is due to the formation of the key titanacyclopentane intermediates F and G having two fused oxatitanacyclopentane rings.

Key words

titanium alkoxides - Grignard reagents - homoallylic alcohols - reductive coupling

7

In some cases, diisopropoxytitanacyclopropane is more smoothly involved in olefin-exchange reactions than 2-substituted titanacyclopropane reagents (see ref. [6] ).

13

Typical procedure: To a solution of homoallylic alcohol 1b (0.86 g, 10 mmol) in Et2O (15 mL) Ti(i-PrO)4 (1.5 mL, 5 mmol) and i-PrMgBr (20 mmol of 1.2-1.5 M solution in Et2O) were added consequently dropwise in 30 min at room temperature, and the mixture was stirred for an additional 30 min. After acidic work up (20 mL of 10% aq. H2SO4) and extraction with ethyl acetate, organic layers were washed with saturated NaHCO3 and brine, dried over MgSO4 and evaporated. 2,9-Decanediol 2b (containing near 10% of 4-methyl-2,8-nonanediol 3b by NMR and GC-MS-analysis) (0.61 g, 70%) was isolated by column chromatography on silica gel (eluent: cyclohexane-ethyl acetate). After two crystallisations (petroleum ether-benzene) 0.38 g of crystalline 2,9-decanediol 2b was obtained: mp 32-33 °C. (lit. [19] mp 33 °C); 1H NMR (400 MHz, CDCl3): δ = 1.17 (d, 6 H, J = 6.4 Hz), 1.20-1.48 (m, 12 H), 2.07 (br s, 2 H), 3.68-3.78 (m, 2 H); 13C NMR (100 MHz, CDCl3) δ = 23.33, 25.57, 29.48, 39.18, 67.89; MS (70 eV) 29, 45 (100%), 55, 69, 81, 96, 112, 123, 141, 155; IR (CCl4, cm-1) 3600.

15

Selected NMR data of the reductive coupling products: 1-[6-(1-Hydroxycyclopentyl)hexyl]-1-cyclopentanol ( 2d): 13C NMR (100 MHz, CDCl3): δ = 23.79, 24.59, 30.18, 39.64, 41.47, 82.51. (2 E , 12 E )-2,12-Tetradecadiene-4,11-diol ( 2e): 1H NMR (400 MHz, CDCl3): δ = 1.20-1.38 (m, 8 H), 1.38-1.56 (m, 4 H), 1.67 (d, 6 H, J = 6.4 Hz), 1.72 (br s, 2 H), 3.98 (q, 2 H, J = 6.6 Hz), 5.40-5.48 (m, 2 H), 5.56-5.68 (m, 2 H); 13C NMR (100 MHz, CDCl3): δ = 17.56, 25.32, 29.42, 37.20, 73.00, 126.52, 134.38. 2,9-Dimethyl-2,9-decanediol ( 2c): 1H NMR (400 MHz, CDCl3): δ = 1.12-1.20 (m, 12 H), 1.24-1.36 (m, 4 H), 1.36-1.46 (m, 4 H), 1.50 (br s, 2 H); 13C NMR (100 MHz, CDCl3): δ = 24.22, 29.14, 30.09, 43.89, 70.90. 1,10-Decanediol ( 2g): 1H NMR (400 MHz, CDCl3): δ = 1.22-1.44 (m, 12 H), 1.48-1.64 (m, 4 H), 2.05 (br s, 2 H), 3.61 (t, 4 H, J = 6.6 Hz); 13C NMR (100 MHz, CDCl3): δ = 25.66, 29.31, 29.43, 32.67, 62.85. 2,11-Dodecanediol ( 2h): 1H NMR (400 MHz, CDCl3): δ = 1.17 (d, 6 H, J = 6.4 Hz), 1.24-1.50 (m, 16 H), 1.94 (br s, 2 H), 3.71-3.84 (m, 2 H); 13C NMR (100 MHz, CDCl3): δ = 23.34, 25.65, 29.44, 29.53, 39.25, 67.95.

16

After acidic hydrolysis of the reaction products, diols 3b and 4,5-dimethyl-2,7-octanediol were obtained in 29% yield as an nearly equimolar mixture (GC-MS).