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DOI: 10.1055/s-2004-835664
Cationic Platinum-Catalyzed Etherification by Intra- and Intermolecular Dehydration of Alcohols
Publication History
Publication Date:
29 November 2004 (online)
Abstract
Catalytic etherification of diols proceeds to give various cyclic ethers by use of cationic platinum salt, which is in situ prepared from PtCl2 and AgSbF6. Etherification of benzylic alcohols is also possible by intermolecular dehydration. Both of intra- and intermolecular etherifications smoothly proceed even under an atmosphere of air.
Key words
platinum - ethers - dehydration - diols - alcohols
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References
All of the 2,n-disubstituted cyclic ethers were obtained as a mixture of dl and meso isomers (ca. 1:1).
10Typical Experimental Procedure for Cyclic Ethers from Diols (Table 2): PtCl2 (1.1 mg, 0.004 mmol) was placed in a flask and a 1,2-dichloroethane solution (2.0 mL) of a diol (0.20 mmol, 0.10 M) was added. To the resulting mixture was added AgSbF6 (3.6 mg, 0.010 mmol) and the mixture was stirred at the temperature cited in Table [2] for 0.5-8 h. After excluding the solvent to the volume of ca. 0.5 mL under reduced pressure, the obtained mixture was purified by column chromatography (hexane-EtOAc) using silica gel to give a pure cyclic ether.
112-Methyl-2-(3-phenylpropyl)tetrahydrofuran: IR (neat): 1496, 1454, 1057, 748, 700 cm-1. 1H NMR (400 MHz, CDCl3): δ = 1.16 (s, 3 H), 1.51-1.74 (m, 6 H), 1.82-1.95 (m, 2 H), 2.59-2.66 (m, 2 H), 3.74-3.85 (m, 2 H), 7.17-7.29 (m, 5 H). 13C NMR (100 MHz, CDCl3): δ = 25.8, 26.1, 26.7, 36.5, 36.7, 40.9, 67.1, 82.5, 125.6, 128.1, 128.3, 142.5. HRMS (FAB): m/z calcd for C14H20O [M+]: 204.1514. Found: 204.1508.
12Typical Experimental Procedure for Acyclic Ethers (Table 3): PtCl2 (3.2 mg, 0.012 mmol) was placed in a flask and a 1,2-dichloroethane solution (4.5 mL) of an alcohol (0.30 mmol) and allyl alcohol (0.60 mmol) was added. To the resulting mixture was added AgSbF6 (10.3 mg, 0.030 mmol) and the mixture was stirred at the temperature cited in Table [3] for 1-2 h. The following procedure is the same as in ref. 10.
13Complete racemization of a chiral alcohol indicates that the present etherification proceeded via SN1 pathway (Scheme [1] ).