Synlett 2013; 24(8): 981-986
DOI: 10.1055/s-0032-1316896
letter
© Georg Thieme Verlag Stuttgart · New York

Synthesis of α,β-Alkynyl Esters and Unsymmetrical Maleate Esters Catalyzed by Pd/C; An Efficient Phosphine-Free Catalytic System for Oxidative Alkoxycarbonylation of Terminal Alkynes

Sandip T. Gadge
Department of Chemistry, Institute of Chemical Technology, N. Parekh Marg, Matunga, Mumbai 400 019, India, Fax: +91(22)33611020   eMail: bm.bhanage@gmail.com   eMail: bm.bhanage@ictmumbai.edu.in
,
Bhalchandra M. Bhanage*
Department of Chemistry, Institute of Chemical Technology, N. Parekh Marg, Matunga, Mumbai 400 019, India, Fax: +91(22)33611020   eMail: bm.bhanage@gmail.com   eMail: bm.bhanage@ictmumbai.edu.in
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Publikationsverlauf

Received: 27. Februar 2013

Accepted after revision: 17. März 2013

Publikationsdatum:
28. März 2013 (online)


Abstract

Pd/C-catalyzed oxidative alkoxycarbonylation of terminal alkynes using alcohols in the presence of tetrabutylammonium iodide under CO/O2 (5:1 atm) has been investigated. The desired α,β-alkynyl esters and unsymmetrical maleate esters are formed in good to excellent yields under different reaction conditions. The present protocol eliminates the use of phosphine ligands and has straightforward catalyst recovery. The catalyst was recycled up to six times without significant loss of catalytic activity.

Supporting Information

 
  • References and Notes

  • 7 Gadge ST, Khedkar MV, Lanke SR, Bhanage BM. Adv. Synth. Catal. 2012; 354: 2049
  • 9 See Table 1 of the Supporting Information for catalyst screening and loading.
  • 12 Oxidative Alkoxycarbonylation of Terminal Alkynes; General Procedure: To a 100 mL stainless steel autoclave, the alk-1-yne (1 mmol), the alcohol (0.5 mL), 10% Pd/C (10 mol%), TBAI (0.6 mmol), and 1,4-dioxane (10 mL) were added. The autoclave was closed and pressurized with oxygen (1 atm) and CO (5 atm) without flushing. The reaction mixture was stirred (550 rpm) and heated at 80 °C for 8 h. The reactor was then cooled to r.t. and the pressure released. The reaction mixture was filtered and the filtrate was washed with saturated sodium thiosulphate (3 × 4 mL), dried over Na2SO4, filtered and the solvent evaporated. The crude product was purified by column chromatography. Ethyl 3-[4(Trifluoromethyl)phenyl]propiolate (3j): 13 Yield: 83%; colorless liquid; IR (neat): 2253, 1711 cm–1; GCMS (EI, 70 eV): m/z (%) = 242 (7) [M+], 223 (3), 197 (100), 170 (67), 147 (7); 1H NMR (300 MHz, CDCl3): δ = 7.71–7.59 (m, 4 H, ArCH), 4.32 (q, J = 6.9 Hz, 2 H, CH 2CH3), 1.46 (t, J = 6.9 Hz, 3 H, CH2CH 3). Ethyl 3-(Pyren-2-yl)propiolate (3l): Yield: 85%; yellowish solid; IR (KBr): 2205, 1704 cm–1; 1H NMR (400 MHz, CDCl3): δ = 8.57 (d, J = 9.1 Hz, 1 H, ArCH), 8.27–8.04 (m, 8 H, ArCH), 4.40 (q, J = 7.1 Hz, 2 H, CH 2CH3), 1.44 (t, J = 7.1 Hz, 3 H, CH2CH 3); 13C NMR (75 MHz, CDCl3): δ = 154.30, 133.26, 132.63, 130.69, 130.63, 130.48, 129.14, 129.02, 126.74, 126.23, 126.13, 125.99, 124.53, 124.11, 123.76, 123.53, 113.08, 85.94, 85.59, 62.05, 14.17; HRMS (ESI): m/z calcd. for [C21H14O2Na]+: 321.0886; found: 321.0879. Diethyl 2-(Pyridin-3-yl)maleate (4g): Yield: 89%; yellowish liquid; IR (neat): 1723, 1629 cm–1; 1H NMR (300 MHz, CDCl3): δ = 8.76 (d, J = 1.8 Hz, 1 H, ArCH), 8.67–8.65 (m, 1 H, ArCH), 7.86–7.82 (m, 1 H, ArCH), 7.41–7.37 (m, 1 H, ArCH), 6.35 (s, 1 H, COCH=CCO), 4.43 (q, J = 6.9 Hz, 2 H, CH3CH 2O), 4.26 (q, J = 6.9 Hz, 2 H, CH3CH 2O), 1.38 (t, J = 6.9 Hz, 3 H, CH 3CH2O), 1.33 (t, J = 6.9 Hz, 3 H, CH 3CH2O); 13C NMR (75 MHz, CDCl3): δ = 166.92, 164.44, 150.60, 147.40, 145.12, 134.60, 130.11, 123.92, 120.14, 62.32, 61.38, 14.22, 14.06; GCMS (EI, 70 eV): m/z (%) = 249 (13) [M+], 220 (78), 204 (55), 192 (16), 176 (91), 148 (100), 132 (25), 120 (18), 104 (56), 76 (33), 50 (24); HRMS (ESI): m/z calcd. for [C13H15O4N + H]+: 250.1074; found: 250.1070.
  • 13 Butt G, Topsom RD. Spectrochim. Acta, Part A 1982; 38: 649