Cationic Platinum-Catalyzed Etherification by Intra- and Intermolecular Dehydration of Alcohols

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.

platinum - ethers - dehydration - diols - alcohols

References

<A NAME="RU26004ST-1A">1a</A> Feuer H. Hooz J. In The Chemistry of the Ether Linkage   Patai S. John Wiley and Sons; London: 1967.  Chap. 10. p.445 

<A NAME="RU26004ST-1B">1b</A> Baggett N. In Comprehensive Organic Chemistry   Vol. 1:  Barton D. Ollis WD. Pergamon Press; Oxford: 1979.  p.799 

<A NAME="RU26004ST-2">2</A> Molnár A. Felföldi K. Bartók M. Tetrahedron  1981,  37:  2149 

<A NAME="RU26004ST-3">3</A> Scott LT. Naples JO. Synthesis  1973,  209 

<A NAME="RU26004ST-4">4</A> Olah GA. Fung AP. Malhorta R. Synthesis  1981,  474 

<A NAME="RU26004ST-5">5</A> Kim S. Chung KN. Yang S. J. Org. Chem.  1987,  52:  3917 

<A NAME="RU26004ST-6A">6a</A> Zhu Z. Espenson JH. J. Org. Chem.  1996,  61:  324 

<A NAME="RU26004ST-6B">6b</A> Salehi P. Iranpoor N. Behbahani FK. Tetrahedron  1998,  54:  943 

<A NAME="RU26004ST-6C">6c</A> Sharma GVM. Mahalingam AK. J. Org. Chem.  1999,  64:  8943 

<A NAME="RU26004ST-6D">6d</A> Ooi T. Ichikawa H. Itagaki Y. Maruoka K. Heterocycles  2000,  52:  575 

<A NAME="RU26004ST-6E">6e</A> Bouquillon S. Hénin F. Muzart J. Organometallics  2000,  19:  1434 

<A NAME="RU26004ST-6F">6f</A> Kawada A. Yasuda K. Abe H. Harayama T. Chem. Pharm. Bull.  2002,  50:  380 

<A NAME="RU26004ST-6G">6g</A> Miller KJ. Abu-Omar MM. Eur. J. Org. Chem.  2003,  1294 

<A NAME="RU26004ST-6H">6h</A> Noji M. Ohno T. Fuji K. Futaba N. Tajima H. Ishii K. J. Org. Chem.  2003,  68:  9340 

<A NAME="RU26004ST-6I">6i</A> Kayaki Y. Koda T. Ikariya T. J. Org. Chem.  2004,  69:  2595 

Non-dehydrative ether syntheses of propargyl alcohols catalyzed by transition metal complexes:

<A NAME="RU26004ST-7A">7a</A> Nishibayashi Y. Wakiji I. Hidai M. J. Am. Chem. Soc.  2000,  122:  11019 

<A NAME="RU26004ST-7B">7b</A> Sherry BD. Radosevich AT. Toste FD. J. Am. Chem. Soc.  2003,  125:  6076 

Recent examples using platinum salt as Lewis acid catalysts:

<A NAME="RU26004ST-8A">8a</A> Hartman JW. Sperry L. Tetrahedron Lett.  2004,  45:  3787 

<A NAME="RU26004ST-8B">8b</A> Marion F. Coulomb J. Courillon C. Fensterbank L. Malacria M. Org. Lett.  2004,  6:  1509 

<A NAME="RU26004ST-8C">8c</A> Shimada T. Nakamura I. Yamamoto Y. J. Am. Chem. Soc.  2004,  126:  10546 

<A NAME="RU26004ST-8D">8d</A> Nevado C. Ferrer C. Echavarren AM. Org. Lett.  2004,  6:  3191 

<A NAME="RU26004ST-8E">8e</A> Qian H. Han X. Widenhoefer RA. J. Am. Chem. Soc.  2004,  126:  9536 

<A NAME="RU26004ST-9">9</A>

All of the 2,n-disubstituted cyclic ethers were obtained as a mixture of dl and meso isomers (ca. 1:1).

<A NAME="RU26004ST-10">10</A>

Typical 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.

<A NAME="RU26004ST-11">11</A>

2-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.

<A NAME="RU26004ST-12">12</A>

Typical 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.

<A NAME="RU26004ST-13">13</A>

Complete racemization of a chiral alcohol indicates that the present etherification proceeded via S_N1 pathway (Scheme [1] ).