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Synlett 2003(3): 0377-0381
DOI: 10.1055/s-2003-37115
LETTER
© Georg Thieme Verlag Stuttgart · New York

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;
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Publication History

Received 20 November 2002
Publication Date:
07 February 2003 (online)

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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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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%).

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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.

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Khan, A. T.; Mondal, E.; Ghosh, S., unpublished results.

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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.