Regioselective Synthesis of
5-Chlorosalicylates by One-Pot Cyclization of 1,3-Bis(trimethylsilyloxy)buta-1,3-dienes
with 2-Chloro-3-ethoxy-2-alken-1-ones

Olumide Fatunsin; Mohanad Shkoor; Sergé-Mithérand Tengho Toguem; Abdolmajid Riahi; Olapeju O. Aiyelaagbe; Emmanuel T. Akintayo; Christine Fischer; Peter Langer

doi:10.1055/s-0030-1258488

LETTER

Regioselective Synthesis of 5-Chlorosalicylates by One-Pot Cyclization of 1,3-Bis(trimethylsilyloxy)buta-1,3-dienes with 2-Chloro-3-ethoxy-2-alken-1-ones

Olumide Fatunsin^a, Mohanad Shkoor^a, Sergé-Mithérand Tengho Toguem^a, Abdolmajid Riahi^a, Olapeju O. Aiyelaagbe^c, Emmanuel T. Akintayo^d, Christine Fischer^b, 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
^c Department of Chemistry, University of Ibadan, Ibadan 200284, Nigeria
^d Department of Chemistry, University of Ado-Ekiti, P.M.B 5363, Ado-Ekiti, Nigeria

Abstract

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Abstract

A variety of 5-chlorosalicylates were prepared by regioselective one-pot cyclizations of 1,3-bis(trimethylsilyloxy)buta-1,3-dienes with novel 2-chloro-3-ethoxy-2-alken-1-ones.

Key words

organochlorine compounds - cyclizations - silyl enol ethers - arenes

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References

References and Notes

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For a review of 1,3-bis(trimethylsilyloxy)-1,3-dienes in general, see:

<A NAME="RD06610ST-7A">7a</A> For a review of [3+3] cyclizations, see: Langer P. Synthesis 2002, 441

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General Procedure for the Synthesis of 2a-f
To a solution of 1a-f (1 equiv) in Ac₂O (3 equiv) was added triethyl orthoformate (3 equiv). The mixture was heated for 15 h at 140 ˚C. The mixture was dried in vacuo and was purified by chromatography (silica gel, heptanes-EtOAc) to give 2a-f.

2-Chloro-3-ethoxy-1-phenylprop-2-en-1-one (2a) A mixture of 1a (2.00 g, 12.9 mmol), triethyl orthoformate (6.5 mL, 38.8 mmol) and Ac₂O (3.7 mL, 38.8 mmol), was refluxed for 15 h at 140 ˚C, and the resultant mixture was purified by chromatography (silica gel, n-heptane-EtOAc) to give 2a as a brownish oil (2.10 g, 76%). ^¹H NMR (300 MHz, CDCl₃): δ = 1.32 (t, ^³ J = 7.1 Hz, 3 H, OCH₂CH ₃), 4.10 (q, ^³ J = 7.1 Hz, 2 H, OCH ₂CH₃), 7.37-7.44 (m, 4 H, CH, CH_Ar), 7.52-7.55 (m, 2 H, CH_Ar). ^¹³C NMR (75 MHz, CDCl₃): δ = 15.3 (CH₃), 66.0 (OCH₂), 113.8 (CCl), 128.7 (2 × CH_Ar), 128.8 (2 × CH_Ar), 134.0 (CH_Ar), 138.2 (C_Ar), 160.5 (CH), 189.5 (CO). IR (neat): 3368 (w), 3062 (w), 2980 (w), 2935 (w), 1747 (m), 1691 (s), 1596 (m), 1449 (m), 1372 (m), 1216 (s), 1181 (m), 1085 (m), 1000 (m), 965 (m), 846 (m), 754 (m), 686 (s), 640 (m), 600 (m), 561 (m) cm^-¹. Anal. Calcd for C₁₁H₁₁O₂Cl: C, 62.66; H, 5.22. Found: C, 62.85; H, 5.03.

General Procedure for the Synthesis of 4a-q To a CH₂Cl₂ solution (2 mL/1.0 mmol of 2a-f) of 2a-f was added 3a-d (1.1 mmol) and, subsequently, TiCl₄ (1.1 mmol) at -78 ˚C. The temperature of the solution was allowed to warm to 20 ˚C over 12 h with stirring. HCl (10%, 20 mL) was added to the solution, and the organic and the aqueous layers were separated. The latter was extracted with CH₂Cl₂ (3 × 20 mL). The combined organic layers were dried (Na₂SO₄), filtered, and the filtrate was concentrated in vacuo. The residue was purified by chromatography (silica gel, heptanes-EtOAc) to give 4a-q.

Methyl 6-Chloro-3-hydroxybiphenyl-2-carboxylate (4a) Starting with 2a (316 mg, 1.5 mmol) and 3a (430 mg, 1.65 mmol), 4a was isolated after chromatography (silica gel, n-heptane-EtOAc) as a yellowish oil (177 mg, 45%). ^¹H NMR (300 MHz, CDCl₃): δ = 3.32 (s, 3 H, OCH₃), 6.92 (d, ^³ J = 8.9 Hz, 1 H, CH_Ar), 7.05-7.08 (m, 2 H, CH_Ar), 7.27-7.35 (m, 3 H, CH_Ar), 7.42 (d, ^³ J = 8.9 Hz, 1 H, CH_Ar), 10.65 (s, 1 H, OH). ^¹³C NMR (75 MHz, CDCl₃): δ = 51.0 (OCH₃), 113.1 (CCOOCH₃), 117.4 (CH_Ar), 124.0 (CCl), 126.2 (CH_Ar), 126.6 (2 × CH_Ar), 127.5 (2 × CH_Ar), 134.1 (CH_Ar), 138.7, 140.8 (C_Ar), 159.2 (COH), 169.6 (CO). IR (neat): 3058 (w), 3025 (w), 2951 (w), 2925 (w), 2852 (w), 1739 (w), 1666 (s), 1593 (m), 1499 (w), 1435 (s), 1334 (m), 1289 (m), 1206 (s), 1135 (m), 1093 (m), 1027 (w), 1000 (w), 963 (m), 825 (m), 770 (m), 748 (s), 698 (s), 690 (s), 635 (m), 610 (m), 573 (m) cm^-¹. GC-MS (EI, 70 eV): m/z (%) = 262 (^³5Cl, 68) [M]⁺, 230 (100), 202 (63), 168 (11), 139 (81), 113 (6), 87 (7), 69 (8). HRMS (EI): m/z calcd for C₁₄H₁₁O₃ ^³5Cl [M]⁺: 262.03912; found: 262.03916.

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