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Synlett 2004(10): 1686-1690  
DOI: 10.1055/s-2004-829558
LETTER
© Georg Thieme Verlag Stuttgart · New York

Oxidative Deprotection of 1,3-Dithiane Group Using NaClO2 and NaH2PO4 in Aqueous Methanol

Takahiro Ichigea, Annu Miyakea, Naoki Kanoha,b, Masaya Nakata*a
a Department of Applied Chemistry, Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan
Fax: +81(45)5661551; e-Mail: msynktxa@applc.keio.ac.jp;
b Antibiotics Laboratory, Discovery Research Institute, RIKEN (The Institute of Physical and Chemical Research), 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
Further Information

Publication History

Received 17 May 2004
Publication Date:
15 July 2004 (online)

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Abstract

The 1,3-dithiane group was oxidatively deprotected ­under the conditions of sodium chlorite, sodium dihydrogenphosphate, and 2-methyl-2-butene in 3:1 methanol-water at room temperature in good yield.

Key words

thioacetals - sodium chlorite - sodium dihydrogenphosphate - protecting groups - deprotection

7

Total synthesis of biscembranoid marine natural product, methyl sarcoate, and the synthesis of 1 will be reported elsewhere.

9

The starting material 3a remained when less than 6 molar amounts of NaClO2 were used.

10

In the absence of NaH2PO4, no reaction occurred.

12

The sulfenic acid part in II is a transient structure because of its high reactivity. See ref. [14]

13

The ratio was based on 1H NMR analysis of the crude product. Methyl ester 5 was obtained in only a trace amount.

15

Representative Experimental Procedure (Table 2, Entry 2):
To a mixture of 3a (57.0 mg, 0.163 mmol) in MeOH (1.2 mL) and H2O (0.400 mL) were added at r.t. 2-methyl-2-butene (0.172 mL, 1.630 mmol) and NaH2PO4 (39.0 mg, 0.326 mmol). After cooling to 0 °C, 86% NaClO2 (103.0 mg, 0.978 mmol) was added and the resulting suspension was stirred at r.t. for 2 h. Then H2O (1.5 mL) was added and the mixture was extracted with EtOAc (1.5 ml × 3); the extracts were washed with sat. aq NaCl, dried with Na2SO4, and concentrated. The residue was chromatographed on silica gel with 3:1 hexane-EtOAc to afford 4a (38.7 mg, 92%) as a colorless oil. Compound 4a: 1H NMR (300 MHz, CDCl3, CHCl3 = 7.26): δ = 0.04 (6 H, s), 0.87 (9 H, s), 0.88 (3 H, t, J = 7.0 Hz), 1.18-1.40 (4 H, m), 1.57 (2 H, quint, J = 7.5 Hz), 2.44 (2 H, t, J = 7.5 Hz), 2.59 (2 H, t, J = 7.0 Hz), 3.88 (2 H, t, J = 7.0 Hz). 13C NMR (75 MHz, CDCl3 = 77.16): δ = -5.35, 14.04, 18.34, 22.59, 23.34, 25.98, 31.52, 43.99, 45.70, 59.07, 210.42. HRMS (EI): m/z calcd for C10H21O2Si [M - t-Bu]+ 201.1311; found: 201.1318.