Synlett 2011(19): 2862-2866  
DOI: 10.1055/s-0031-1289857
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Iron-Catalyzed Reductive Dehydroxylation of Benzylic Alcohols Using Polymethylhydrosiloxane (PMHS)

Li Yan Chan, Jazreel Seh Kai Lim, Sunggak Kim*
Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore
Fax: +65(6791)1961; e-Mail: sgkim@ntu.edu.sg;
Further Information

Publication History

Received 12 August 2011
Publication Date:
09 November 2011 (online)

Abstract

The combination of FeCl3 and PMHS is an efficient reducing system for the selective dehydroxylation of secondary benzylic alcohols, even in the presence of carbonyls, under very mild conditions.

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General procedure for the reductive dehydroxylation of benzylic alcohols 4: Anhydrous FeCl3 (2.4 mg, 0.015 mmol, 5 mol% equiv) was carefully weighed and stirred in 1,2-dichloroethane (2 mL) for 5 min. PMHS (0.05 mL, 0.9 mmol, 3.0 equiv) was then added to the prepared catalyst solution, followed by benzylic alcohol 4 (0.3 mmol, 1.0 equiv) and stirred at either r.t. or heated to the respective temperature. The residual crude product was concentrated in vacuo and purified by flash chromatography to afford the desired product 5. ¹H NMR and ¹³C NMR data of previously unknown compounds: 4-heptyl-1,2-dimethoxybenzene (5d). ¹H NMR (400 MHz, CDCl3): δ = 7.26-6.70 (m, 3 H), 3.87 (s, 3 H), 3.85 (s, 3 H), 2.54 (t, J = 7.8 Hz, 2 H), 1.60-0.86 (m, 13 H); ¹³C NMR (100 MHz, CDCl3): δ = 148.7, 147.0, 135.6, 120.1, 111.8, 111.2, 55.9, 55.8 35.6, 31.8, 31.7, 29.3, 29.2, 22.7, 14.1; HRMS (ESI): m/z [M + 1] calcd for C15H25O2: 237.1855; found: 237.1850. 1-Bromo-4-heptyl-benzene (5k):¹¹ ¹H NMR (400 MHz, CDCl3): δ = 7.37 (d, J = 8.3 Hz, 2 H), 7.03 (d, J = 8.3 Hz, 2 H), 2.54 (t, J = 7.8 Hz, 2 H), 1.63-1.53 (m, 2 H), 1.36-1.19 (m, 8 H), 0.88 (t, J = 6.8 Hz, 3 H); ¹³C NMR (100 MHz, CDCl3): δ = 141.8, 131.2, 130.1, 119.2, 35.3, 31.8, 31.3, 29.1, 29.1, 22.6, 14.1; HRMS (ESI): m/z [M + 1] calcd for C13H20Br: 255.0748; found: 255.0757.