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Synlett 2009(9): 1477-1479  
DOI: 10.1055/s-0029-1217177
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Regioselective Synthesis of 2-Arylthio-4-methoxybenzoates by Formal [3+3] Cyclocondensations of 3-Arylthio-1-trimethylsilyloxybuta-1,3-dienes with 3-Oxo-orthoesters

Muhammad Imrana, Inam Iqbala, Peter Langer*a,b
a Institut für Chemie, Universität Rostock, Albert Einstein Str. 3a, 18059 Rostock, Germany
Fax: +49(381)4986412; e-Mail: peter.langer@uni-rostock.de;
b Leibniz-Institut für Katalyse an der Universität Rostock e.V., Albert Einstein Str. 29a, 18059 Rostock, Germany
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Publication History

Received 11 December 2008
Publication Date:
13 May 2009 (online)

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Abstract

A variety of 2-arylthio-4-methoxybenzoates are regio­selectively prepared by the first formal [3+3] cyclocondensations of 3-arylthio-1-trimethylsilyloxybuta-1,3-dienes with 3-oxo-ortho­esters.

Key Words

arenes - cyclizations - diaryl sulfides - regioselectivity - silyl enol ethers

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18

General Experimental Procedure
To a CH2Cl2 soln (3 mL/mmol of 1) of 2 (1.5 mmol) and 1 (2.25 mmol) was added TiCl4 (2.25 mmol) at -78 ˚C. The solution was allowed to warm to 20 ˚C within 20 h. To the solution was added HCl (10%, 25 mL). The organic and the aqueous layer were separated and the latter was extracted with CH2Cl2 (3 × 20 mL). The combined organic layers were dried (Na2SO4), filtered, and the filtrate was concentrated in vacuo, and the residue was purified by chromatography (SiO2, EtOAc-n-heptane = 1:9).
4-Methoxy-6-methyl-2-(3-tolylsulfanyl)benzoic Acid Methyl Ester (3b)
Starting with 1a (2.25 mmol), 2b (1.5 mmol), and TiCl4 (2.25 mmol), 3b was isolated as a yellow oil (226 mg, 50%). ¹H NMR (250 MHz, CDCl3): δ = 2.25 (s, 3 H, CH3), 2.30 (s, 3 H, CH3), 3.69 (s, 3 H, OCH3), 3.87 (s, 3 H, OCH3), 6.57-7.39 (m, 6 H, Ar). ¹³C NMR (63 MHz, CDCl3): δ = 20.4 (CH3), 21.2 (CH3), 51.9 (OCH3), 55.2 (CH3O), 114.1, 114.5, (CHAr), 126.9, 128.3 (C), 129.4, 131.5, 132.1, 133.0 (CHAr), 138.3, 139.1, 140.1, 146.9, 168.8 (C). IR (KBr): ν = 2998 (w), 2947 (w), 2834 (w), 2735 (w), 2570 (w), 1724 (s), 1589 (s), 1564 (m), 15560 (m), 1471 (m), 1426 (m), 1380 (w), 1302 (m), 1264 (s), 1217 (s), 1187 (m), 1136 (s), 1090 (s), 1047 (s), 998 (m), 960 (m), 776 (s), 691 (s), 608 (m). MS (EI): m/z (%) = 302 (100) [M+], 272 (11), 271 (61), 270 (21), 269 (86), 256 (18), 255 (49),228 (17), 227 (13), 184 (15), 121 (3), 91 (4), 65 (5). HRMS (EI): m/z calcd for C17H18O2O3S [M+]: 302.09712; found: 302.097152.