Synlett 2008(16): 2425-2428  
DOI: 10.1055/s-2008-1078215
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

An Efficient and Solvent-Free Synthesis of Mixed Ortho Esters

Kelly L. Cosgrovea, Ross P. McGeary*a,b
a School of Molecular and Microbial Sciences, The University of Queensland, Brisbane, Queensland 4072, Australia
b School of Pharmacy, The University of Queensland, Brisbane, Queensland 4072, Australia
Fax: +61(7)33463249; e-Mail: r.mcgeary@uq.edu.au;
Further Information

Publication History

Received 15 May 2008
Publication Date:
22 August 2008 (online)

Abstract

Primary, secondary and electron-deficient tertiary alcohols react rapidly with ketene dimethyl acetal to form mixed ortho esters, without catalysts and under solvent-free conditions. 1,2-Diols yield bis(mixed ortho esters), rather than cyclic ortho esters.

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Compound 14: light yellow oil. ¹H NMR (400 MHz, CDCl3): δ = 4.59 (s, 2 H), 4.09-4.23 (m, 4 H), 3.27 (s, 6 H), 3.23 (s, 6 H), 1.42 (s, 6 H), 1.26 (t, 6 H, J = 7.2 Hz). ¹³C NMR (100 MHz, CDCl3): δ = 169.8, 115.4, 60.9, 50.33, 50.31, 19.7, 14.1. HRMS (ESI, +ve): m/z [M + Na]+ calcd for C16H30O10: 405.1737; found: 405.1732.

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Compound 16: yellow oil. ¹H NMR (400 MHz, C6D6): δ = 6.00 (ddd, 1 H, ³ J trans = 17.4 Hz, ³ J cis = 10.6 Hz, ³ J = 6.1 Hz), 5.32 (br dt, 1 H, ³ J trans = 17.2 Hz, ² J = 1.5 Hz, 4 J = 1.5 Hz), 5.06 (ddd, 1 H, ³ J cis = 10.6 Hz, ² J = 1.8 Hz, 4 J = 1.4 Hz), 4.57 (qt, 1 H, ³ J = 6.1 Hz, 4 J = 1.3 Hz), 3.79 (dd, 1 H, ² J = 9.7 Hz, ³ J = 6.1 Hz), 3.62 (dd, 1 H, ² J = 9.7 Hz, ³ J = 5.9 Hz), 3.20 (s, 3 H), 3.19 (s, 3 H), 3.17 (s, 3 H), 3.16 (s, 3 H), 1.42 (s, 3 H), 1.34 (s, 3 H). ¹³C NMR (100 MHz, C6D6): δ = 138.7, 128.9, 115.4, 114.8, 72.6, 66.0, 49.8, 49.7, 49.6, 49.5, 20.8, 19.4. MS (ESI): m/z = 287 [M + Na]+. HRMS (ESI, +ve): m/z [M + Na]+ calcd for C12H24O6: 287.1470; found: 287.1454.

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In a typical experiment, ketene dimethyl acetal (3 mmol per hydroxyl group) was added cautiously to the anhyd alcohol (1 mmol) and stirred rapidly at r.t. under argon for 30 min. The reaction was followed by neutral alumina TLC. After complete conversion into the mixed ortho ester, the excess ketene dimethyl acetal was removed in vacuo resulting in pure mixed ortho ester in quantitative yield. Toluene-d 8 and C6D6 were used for most NMR samples because trace amounts of HCl in CDCl3 resulted in decomposition of the mixed ortho ester.³³

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All compounds synthesised were characterised by ¹H, ¹³C NMR and/or HRMS and elemental analysis.