A Highly Efficient Procedure for Regeneration of Carbonyl Groups from their Corresponding Oxathioacetals and Dithioacetals Using Sodium Nitrite and Acetyl Chloride in Dichloromethane

Abu T.  Khan; Ejabul  Mondal; Priti R.  Sahu

doi:10.1055/s-2003-37115

LETTER

A Highly Efficient Procedure for Regeneration of Carbonyl Groups from their Corresponding Oxathioacetals and Dithioacetals Using Sodium Nitrite and Acetyl Chloride in Dichloromethane

Abu T. Khan*, Ejabul Mondal, Priti R. Sahu
Department of Chemistry, Indian Institute of Technology, North Guwahati, Guwahati-781039, Assam, India
Fax: +91(361)2690762; e-Mail: atk@postmark.net;

Abstract

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Abstract

A wide variety of oxathioacetals 1 as well as dithioacetals 2 can be chemoselectively deprotected to the corresponding carbonyl compounds 3 in good yields by employing NaNO₂-AcCl and H₂O in CH₂Cl₂ at 0 °C to room temperature. Some of the major advantages of this procedure are: mild conditions, easy to handle, highly chemoselective and efficient, high yields and inexpensive reagents. In addition, no acetylation occurs at the hydroxyl group nor chlorination takes place at the double bond.

Key words

deprotection - oxathioacetals - dithioacetals - sodium nitrite - acetyl chloride

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References

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A Typical Procedure for Deprotection of Oxathioacetals: The mixture of NaNO₂ (0.069 g, 1 mmol) and AcCl (71 µL, 1 mmol) in CH₂Cl₂ (3 mL) was stirred for 10 min at 0-5 °C. Then the substrate 2-(p-methoxyphenyl)-1,3-oxathiolane 1f (0.196 g, 1 mmol) in CH₂Cl₂ (2 mL) was added into the above reaction mixture at the same temperature. After stirring for 5 min, water (1 mL) was added and the mixture brought to r.t. The reaction was completed with additional stirring 20 min (TLC). Finally, the reaction mixture was neutralized with NaHCO₃ and extracted with CH₂Cl₂ (2 × 15 mL). The organic layer was washed with water (2 × 20 mL) and dried (Na₂SO₄). Evaporation of the solvent gave the crude residue, which was purified by column chromato-graphy on silica gel (eluent: hexane-EtOAc, 19:1). Product 3f was obtained as a colourless liquid 0.122 g (90%).
A Typical Procedure for Deprotection of Dithioacetals: The reaction was carried out with compound 2f as stated above except 2 equiv of NaNO₂ and AcCl (1:1) mixture was used. Product 3f was obtained as a colourless liquid 0.129 g (95%).

Spectroscopic Data for Compound 1d, 1e, 3d and 3e:For 1d: ¹H NMR (400 MHz, CDCl₃): δ = 0.20 (s, 6 H, SiCH₃), 0.97 [s, 9 H, SiC(CH₃)₃], 3.19 (m, 1 H, -CHS-), 3.27 (m, 1 H, -CHS-), 3.94 (m, 1 H, -OCH-), 4.52 (m, 1 H,
-OCH-), 5.99 (s, 1 H, OCHS-), 6.81 (d, 2 H, J = 8.5 Hz, ArH), 7.35 (d, 2 H, J = 8.5 Hz, ArH). ¹³C NMR (100 MHz, CDCl₃): δ = -4.45(2 C), 18.17, 25.64 (3 C), 34.03, 61.20, 87.01, 119.98 (2 C), 128.18 (2 C), 131.46, 156.07. Anal. Calcd for C₁₅H₂₄O₂SSi: C, 60.76; H, 8.16; S, 10.81. Found: C, 60.57; H, 8.10; S, 10.68. For 1e: ¹H NMR (400 MHz, CDCl₃): δ = 3.18 (m, 1 H, -CHS-), 3.28 (m, 1 H, -CHS-), 3.91 (m, 1 H, -OCH-), 4.51 (m, 3 H, -OCH₂-, OCH-), 5.28 (dd, 1 H, J = 1.5 Hz, J = 10.5 Hz, OCH₂CH=CH ₂), 5.40 (dd, 1 H, J = 1.5 Hz, J = 17.3 Hz, OCH₂CH=CH ₂), 5.99 (s, 1 H, OCHS-), 6.05 (m, 1 H, OCH₂ CH=CH₂) 6.95 (d, 2 H, J = 8.7 Hz, ArH), 7.40 (d, 2 H, J = 8.7 Hz, ArH). Anal. Calcd for C₁₂H₁₄O₂S: C, 64.83; H, 6.35; S, 16.22. Found: C, 64.61; H, 6.30; S, 16.10. For 3d: ¹H NMR (400 MHz, CDCl₃): δ = 0.05 (s, 6 H, SiCH₃), 0.79 [s, 9 H, SiC(CH₃)₃], 6.70 (d, 2 H, J = 8.6 Hz, ArH) 7.54 (d, 2 H, J = 8.6 Hz, ArH), 9.94 (s, 1 H, CHO). Anal. Calcd for C₁₃H₂₀O₂: C, 74.96; H, 9.68. Found: C, 74.69; H, 9.57. For 3e: ¹H NMR (400 MHz, CDCl₃): δ = 4.63 (m, 2 H, -OCH ₂-CH=CH₂), 5.34 (dd, 1 H, J = 1.5 Hz, J = 10.5 Hz, OCH₂CH=CH ₂), 5.44 (dd, 1 H, J = 1.5 Hz, J = 17.3 Hz, OCH₂CH=CH ₂), 6.06 (m, 1 H, OCH₂ CH=CH₂) 7.02 (d, 2 H, J = 8.8 Hz, ArH), 7.84 (d, 2 H, J = 8.7 Hz, ArH), 9.88 (s, 1 H, CHO). ¹³C NMR (100 MHz, CDCl₃): δ = 68.95, 114.94 (2 C), 118.34, 129.94, 131.94 (2 C), 132.21, 163.55, 190.81. Anal. Calcd for C₁₀H₁₀O₂: C, 74.06; H, 6.21. Found: C, 73.95; H, 6.15.

Khan, A. T.; Mondal, E.; Ghosh, S., unpublished results.

Spectroscopic Data for Compound 3v and 3w: For 3v: ¹H NMR (300 MHz, CDCl₃): δ = 2.07 (s, 9 H, COCH₃), 2.20 (s, 3 H, COCH₃), 4.19 (dd, 1 H, J = 4.6 Hz, J = 12.6 Hz, H-5′), 4.33 (dd, 1 H, J = 2.6 Hz, J = 12.6 Hz, H-5), 5.27 (m, 1 H, H-4), 5.39 (d, 1 H, J = 2.2 Hz, H-2), 5.69 (dd, 1 H, J = 2.1 Hz, J = 8.8 Hz, H-3), 9.48 (s, 1 H, CHO). Anal. Calcd for C₁₃H₁₈O₉: C, 49.06; H, 5.70. Found: C, 48.88; H, 5.63. For 3w: ¹H NMR (300 MHz, CDCl₃): δ = 1.97 (s, 3 H, COCH₃), 2.06 (s, 3 H, COCH₃), 2.09 (s, 3 H, COCH₃), 2.19 (s, 3 H, COCH₃), 4.17 (dd, 1 H, J = 4.3 Hz, J = 12.6 Hz, H-5′), 4.37 (dd, 1 H, J = 2.6 Hz, J = 12.6 Hz, H-5), 5.31 (m, 1 H, H-4), 5.45 (d, 1 H, J = 2.5 Hz, H-2), 5.61 (dd, 1 H, J = 2.5 Hz, J = 8.8 Hz, H-3), 9.50 (s, 1 H, CHO). Anal. Calcd for C₁₃H₁₈O₉: C,49.06; H, 5.70. Found: C, 48.82; H, 5.74.