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Synlett 2003(11): 1728-1730
DOI: 10.1055/s-2003-41430
LETTER
© Georg Thieme Verlag Stuttgart · New York

A Simple and Efficient Protocol for the Deprenylation of Ethers and Esters Catalysed by Zirconium(IV) Chloride-Sodium Iodide [1]

Gangavaram V. M. Sharma*, Ch. Govardhan Reddy, Palakodety Radha Krishna
D-211, Discovery Laboratory, Organic Chemistry Division III, Indian Institute of Chemical Technology, Hyderabad 500 007, India
Fax: +91(40))27160387/757; e-Mail: esmvee@iict.ap.nic.in;
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Publikationsverlauf

Received 9 July 2003
Publikationsdatum:
22. September 2003 (online)

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Abstract

An efficient protocol for the deprotection of prenyl ethers and esters is developed using 20 mol% ZrCl4-NaI (1:1) in CH3CN as a reagent system. A variety of substrates as well as functional groups well tolerate the present reaction conditions.

Key words

deprenylation - protecting groups - esters - catalytic - zirconium(IV) chloride

1

IICT Communication No. 030201.

1

IICT Communication No. 030201.

17

General Experimental Procedure: A stirred solution of the prenyl ether/ester (1 mmol) in CH3CN (5 mL) was treated with ZrCl4 (0.046 g, 0.2 mmol), NaI (0.03 g, 0.2 mmol) and heated at reflux until complete consumption of the starting material (TLC analysis). The solvent was removed under reduced pressure, the residue dissolved in EtOAc (2 × 10 mL) and washed with H2O (2 × 10 mL) and brine (15 mL). The organic layer was dried (Na2SO4) and evaporated under reduced pressure to afford a crude product which on purification by column chromatography (silica gel, 60-120, EtOAc-hexane, 5:95) furnished alcohol/acid. Spectral data for selected compounds: Compound 4: IR (neat): 1510, 1745, 2362, 2858, 2936 cm-1. 1H NMR (200 MHz, CDCl3): δ = 1.36-1.43 (m, 8 H), 1.68 (s, 3 H), 1.71 (s, 3 H), 2.10 (s, 3 H), 3.57 (t, J = 6.5 Hz, 2 H), 3.88 (d, J = 4.7 Hz, 2 H), 4.05 (t, J = 6.4 Hz, 2 H), 5.29-5.32 (t, J = 6.5 Hz, 1 H). MS (EI): m/z (%) = 228 [M+]. Compound 8: IR (neat): 1376, 1510, 1620, 2932, 2986 cm-1. 1H NMR (200 MHz, CDCl3): δ = 1.38 (s, 6 H), 1.42 (s, 3 H), 1.52 (s, 3 H), 1.68 (s, 3 H), 1.73 (s, 3 H), 3.87 (d, J = 4.6 Hz, 2 H), 4.03 (ddd, J = 4.0, 6.6 Hz, 1 H), 4.25 (ddd, J = 4.0, 4.5 Hz, 2 H), 4.32 (dd, J = 2.5, 5.1 Hz, 1 H), 4.39 (dd, J = 1.5, 8.0 Hz, 1 H), 4.61 (dd, J = 2.5, 8.0 Hz, 1 H), 5.28-5.31 (t, J = 6.5 Hz, 1 H) 5.52 (d, J = 5.1 Hz, 1 H). MS (EI): m/z (%) = 328 [M+]. Compound 6a: IR(neat): 1260, 1510, 1590, 2920, 3515 cm-1. 1H NMR (200 MHz, CDCl3): δ = 1.36-1.64 (m, 8 H), 3.39-3.42 (t, J = 5.6 Hz, 2 H), 3.59-3.63 (t, J = 5.4 Hz, 2 H), 3.92 (d, J = 6.2 Hz, 2 H), 5.18-5.25 (m, 2 H) 5.84-5.86 (m, 1 H). MS (EI): m/z (%) = 158 [M+]. Compound 7a: IR (neat): 1226, 1523, 2862, 2958, 3506 cm-1. 1H NMR (200 MHz, CDCl3): δ = 1.36-1.61 (m, 8 H), 1.72 (d, J = 6.4 Hz, 3 H), 3.37 (t, J = 6.5 Hz, 2 H), 3.62 (t, J = 6.4 Hz, 2 H), 3.96 (d, J = 4.8 Hz, 2 H), 5.61 (m, 2 H). MS (EI): m/z (%) = 172 [M+]. Compound 15: IR (neat): 1220, 1345, 1565, 1745, 2885, 2930 cm-1. 1H NMR (200 MHz, CDCl3): δ = 0.94-1.20 (m, 6 H), 1.77 (s, 3 H), 1.82 (s, 3 H), 2.18 (m, 1 H), 4.31 (m, 1 H), 4.61 (d, J = 6.6 Hz, 2 H), 5.14 (s, 2 H), 5.32 (t, J = 6.4 Hz, 1 H) 7.39 (m, 5 H). MS (EI): m/z (%) = 319 [M+], 252 [M+ - 69]. Compound 16: IR (neat): 1225, 1350, 1545, 1750, 2865, 2935 cm-1. 1H NMR (200 MHz, CDCl3): δ = 1.22 (s, 9 H), 1.77 (s, 3 H), 1.81 (s, 3 H), 2.47 (t, J = 4.8 Hz, 2 H), 3.38 (t, J = 4.6 Hz, 2 H), 4.56 (d, J = 6.4 Hz, 2 H), 5.10 (br s, 1 H) 5.31 (t, J = 6.4 Hz, 1 H). MS (EI): m/z (%) = 258 [M+ + 1].