Synlett 2018; 29(16): 2208-2212
DOI: 10.1055/s-0037-1610247
letter
© Georg Thieme Verlag Stuttgart · New York

Chemoselective and Metal-Free Synthesis of Aryl Esters from the Corresponding Benzylic Alcohols in Aqueous Medium Using TBHP/TBAI as an Efficient Catalytic System

Sneha Nandy
a   Department of Chemistry, Organic Chemistry Section, Jadavpur University, Kolkata-700032, India   Email: snehanandy6@gmail.com   Email: sanjay.bhar@jadavpuruniversity.in   Email: sanjaybharin@yahoo.com
,
Avishek Ghatak
b   Department of Chemistry, Dr. A. P. J. Abdul Kalam Govt. College, NewTown, Kolkata- 700156, India   Email: avishekghatak26@gmail.com
,
Asit Kumar Das
c   Department of Chemistry, Krishnath College, Berhampore, Murshidabad-742101, India   Email: akdas.chem@gmail.com
,
Sanjay Bhar*
a   Department of Chemistry, Organic Chemistry Section, Jadavpur University, Kolkata-700032, India   Email: snehanandy6@gmail.com   Email: sanjay.bhar@jadavpuruniversity.in   Email: sanjaybharin@yahoo.com
› Author Affiliations
S. N. thanks DST-INSPIRE, India for junior research fellowship. Financial support from UGC-CAS-II program in Chemistry and DST-PURSE-II program at Jadavpur University as well as Infrastructural support from DST-FIST program are gratefully acknowledged.
Further Information

Publication History

Received: 09 July 2018

Accepted after revision: 23 July 2018

Publication Date:
12 September 2018 (online)


Abstract

A novel and transition-metal-free strategy has been developed for the synthesis of aryl esters starting from corresponding benzylic primary alcohols as the exclusive substrates using tert-butyl hydroperoxide (TBHP) as a terminal oxidant in the presence of catalytic amount of tetrabutylammonium iodide (TBAI) and imidazole, where the aliphatic alcohols remained unaffected. These reactions are highly chemoselective and associated with high yield and wide applicability accommodating a wide range of substituents. Excellent chemoselectivity has also been demonstrated through intramolecular competition experiments. This protocol can be considered as an important analogue of Tishchenko reaction using benzylic alcohols as the substrates instead of benzaldehydes.

 
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  • 17 Representative Procedure for the Reaction To a mixture of benzyl alcohol (108 mg, 1.0 mmol) and TBHP (180 mg, 2.0 mmol) in water (5 ml), the catalyst TBAI (73.8 mg, 0.2 mmol) and imidazole (136 mg, 2.0 mmol) were added, and the mixture was stirred at 80 °C for 8 h. The progress of the reaction was monitored by thin layer chromatography (TLC). After completion of reaction, the reaction mixture was cooled to room temperature. Then the organic product was extracted with ethyl acetate (3 × 10 ml), repeatedly washed with distilled water (4 × 5 ml) to remove the unreacted TBHP, dried with anhydrous sodium sulfate, and the solvent was evaporated under reduced pressure to afford benzyl benzoate (182 mg, yield 86%). To a mixture of benzyl alcohol (108 mg, 1.0 mmol) and TBHP (180 mg, 2.0 mmol) in water (3 ml), the catalyst TBAI (73.8 mg, 0.2 mmol), imidazole (136 mg, 2.0 mmol), and MeOH (2 ml) were added, and the mixture was stirred at 80 °C for 8 h. The progress of the reaction was monitored by TLC. After completion of reaction, the reaction mixture was cooled to room temperature. Then MeOH was distilled out, and the organic product was extracted with ethyl acetate (3 × 10 ml), repeatedly washed with distilled water (4 × 5 ml) to remove the unreacted TBHP, dried with anhydrous sodium sulfate, and the solvent was evaporated under reduced pressure to afford methyl benzoate (112 mg, yield 82%).
  • 18 Spectral and Analytical Data of some Representative Compounds (Thiophen-2-yl) Methyl Thiophene-2-carboxylate (2c) Yellow oil (yield 85%).1H NMR (300 MHz, CDCl3): δ = 5.47 (2 H, s), 7.00–7.02 (1 H, m), 7.07–7.10 (1 H, m), 7.17–7.18 (1 H, m), 7.33–7.35 (1 H, m) 7.55–7.57 (1 H, m), 7.82–7.83 (1 H, m). 13C NMR (75 MHz, CDCl3): δ = 61.1, 126.8, 126.9, 127.7, 128.3, 132.7, 133.4, 133.7, 137.7, 161.9. HRMS (ESI-TOF): m/z calcd for C10H8O2S2 [M + Na+]: 246.9866; found: 246.9868. Methyl Benzo[1,3]dioxole-5-carboxylate (6n) Colorless viscous oil (yield 80%). 1H NMR (300 MHz, CDCl3): δ = 3.89 (3 H, s), 6.05 (2 H, s), 6.82 (1 H, d, J = 8.8 Hz), 7.45 (1 H, d, J = 1.4 Hz), 7.64 (1 H, dd, J1 = 9.0 Hz, J2 = 1.5Hz). 13C NMR (75 MHz, CDCl3): δ = 51.9, 101.7, 107.9, 109.5, 124.2, 125.3, 147.7, 151.6, 166.4. Methyl 4-(2-Acetoxyethoxy)benzoate (9) White solid (mp 76 °C; yield 82%). 1H NMR (300 MHz, CDCl3): δ = 2.10 (3 H, s), 3.87 (3 H, s), 4.22–4.23 (2 H, m), 4.44 (2 H, t, J = 4.3 Hz), 6.92 (2 H, d, J = 8.7 Hz), 7.99 (2 H, d, J = 8.7 Hz). 13C NMR (75 MHz, CDCl3): δ = 20.8, 51.9, 62.5, 65.9, 114.1, 123.1, 131.6, 162.2, 166.7, 170.9. HRMS (ESI-TOF): m/z calcd for C12H14O5 [M + Na+]: 261.0741; found: 261.0736 1-[4-(2-Hydroxyethoxy)phenyl]ethanone (11) Yellowish oil (yield 88%). 1H NMR (300 MHz, CDCl3): δ = 2.54 (3 H, s), 3.98 (2 H, t, J = 4.3 Hz), 4.13 (2 H, t, J = 4.4 Hz), 6.93 (2 H, d, J = 8.7 Hz), 7.91 (2 H, d, J = 8.7 Hz). 13C NMR (75 MHz, CDCl3): δ = 29.6, 61.7, 72.2, 114.7, 129.1, 130.1, 162.3, 200.4. HRMS (ESI-TOF): m/z calcd for C10H12O3 [M + Na+]: 203.0687; found: 203.0684 2-(4-Acetyl-phenoxy) Ethyl Acetate (12) Colorless semisolid (yield 85%). 1H NMR (300 MHz, CDCl3): δ = 2.08 (3 H, s), 2.54 (3 H, s), 4.13–4.23 (2 H, m), 4.43 (2 H, t, J = 4.4 Hz), 6.93 (2 H, d, J = 8.6 Hz), 7.92 (2 H, d, J = 8.6 Hz). 13C NMR (75 MHz, CDCl3): δ = 20.8, 26.3, 62.5, 66.0, 114.2, 130.6, 130.7, 162.3, 170.9, 196.7. HRMS (ESI-TOF): m/z calcd for C12H14O4 [M + K+]: 261.1872; found: 261.1876.