Manganese-Promoted β-Elimination Reactions: Totally Stereoselective Synthesis of (E)-α,β-Unsaturated Esters

Abstract

Stereoselective β-elimination of 2-bromo-3-hydroxy­esters is achieved by using non-preactivated manganese and tri­methylsilyl chloride, to yield (E)-α,β-unsaturated esters with total diastereoselectivity.

Key words

alkenes - diastereoselectivity - esters - eliminations - manganese

References and Notes

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• 11c

  See also ref. 7, 9c.

• 12a Typical Procedure for Compound 2h. When a solution of 1h (0.4 mmol, 1 equiv) in dry THF (2.5 mL), in the presence of Mn granules (325 mesh, 0.6 mmol, 1.5 equiv), and TMSCl (0.7 mmol, 1.75 equiv), was refluxed for 5 h, compound 2h was obtained after hydrolysis with >98 % de and 91% yield. For spectroscopic data of 1h see ref. 12b.Compound 2h: ¹H NMR (300 MHz, CDCl₃): δ = 7.52-7.27 (6 H, m), 7.09 (1 H, dd, J = 15.3, 10.9 Hz), 6.89 (1 H, d, J = 15.3 Hz), 4.26 (2 H, q, J = 7.4 Hz), 2.53 (2 H, t, J = 7.4 Hz), 1.61-1.29 (8 H, m), 1.35 (3 H, t, J = 7.4 Hz), 0.92 (3 H, t, J = 6.1 Hz). ¹³C NMR (75 MHz, CDCl₃): δ = 168.1 (C), 138.9 (CH), 138.1 (C), 136.5 (C), 132.5 (CH), 128.7 (CH), 128.5 (CH), 126.9 (CH), 123.7 (CH), 60.4 (CH₂), 31.5 (CH₂), 29.7 (CH₂), 29.1 (CH₂), 27.0 (CH₂), 22.5 (CH₂), 14.2 (CH₃), 14.0 (CH₃). HRMS: m/z calcd for C₁₉H₂₆O₂: 286.1933; found: 286.1904. IR (neat): 2958, 2871, 1461, 1375 cm^-1
• 12b Concellón JM. Bernad PL. Rodríguez-Solla H. Angew. Chem. Int. Ed.  2001,  40:  3897 
• 13 Concellón JM. Concellón C. Méjica C. J. Org. Chem.  2005,  70:  6111 ; see also ref. 2, 3, 12
• Manganese(II) enolates and related species have been proposed as intermediates in other manganese-promoted transformations. See:
• 14a Dessole G. Bernardi L. Bonini BF. Capitò E. Fochi M. Herrera RP. Ricci A. Cahiez G. J. Org. Chem.  2004,  69:  8525 
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• 14c Cahiez G. Figadère B. Cléry P. Tetrahedron Lett.  1994,  35:  6295 
• 15 Similar transition state models have been proposed to explain the selectivity in other Mn(II)-promoted reactions: Oshima K. J. Organomet. Chem.  1999,  575:  1 

4

Aldrich catalogue (2005-2006): manganese (325 mesh): 250 g - 30.50 ı; samarium (40 mesh): 50 g - 325.20 ı; chromium dichloride: 25 g - 541.80 ı.