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Organic Synteses vol 70 - Meyers A.I.

Meyers A.I. , Boecman R.K. Organic Synteses vol 70 - John Wiley & Sons, 1992. - 163 p.
ISBN 0-471-57743
Download (direct link): organicsynthesesvol701992.pdf
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formation at the 2-position. For 5-substitued tetrahydrofurans, significant transselectivity is only observed with large substituents.
O S02Ph
Phx O S02Ph
Ci 0-0
0^^S02Ph O^
Ph'/^O^uS02Ph „-0
ACO. Ac0V^5s.
V^l 6R : 6S
A'°xAAs02Ph Ac0xA)APh 17183
.. ^ Xl. cisitrans
MeO^o S02Ph MeOAoAPh 50:50 91
The benzenesulfones also undergo nucleophilic displacement with silyl enol ethers and ketene silyl acetals in the presence of a Lewis acid such as aluminum trichloride (Scheme 2).8
1. Department of Chemistry, Imperial College of Science, Technology and Medicine, South Kensington, London, SW7 2AY, UK
2. Zelinski, R.; Louvar, J. J. Org. Chem. 1958, 23, 807.
3. Brown, D. S.; Bruno, M.; Davenport, R. J.; Ley, S. V. Tetrahedron 1989, 45, 4293.
4. Ley, S. V.; Lygo, B.; Wonnacott, A. Tetrahedron Lett. 1985, 26, 535; Ley, S. V.; Lygo, B.; Sternfeld, F.; Wonnacott, A. Tetrahedron 1986, 42, 4333.
5. Greek, C.; Grice, P.; Ley, S. V.; Wonnacott, A. Tetrahedron Lett. 1986, 27, 5277.
6. Brown, D. S.; Ley, S. V.; Vile, S. Tetrahedron Lett. 1988, 29, 4873.
7. Brown, D. S.; Ley, S. V. Tetrahedron Lett. 1988, 29, 4869.
8. Brown, D. S.; Ley, S. V.; Bruno, M. Heterocycles 1989, 28, 773.
Scheme 2
Chemical Abstracts Nomenclature (Collective Index Number); (Registry Number)
Tetrahydro-2-(phenylethynyl)-2H-pyran: 2H-Pyran, tetrahydro-2-(phenyiethynyl)-
(10); (70141-82-1)
Phenylacetylene: Benzene, ethynyl- (8,9); (536-74-3)
Isopropylmagnesium chloride: Magnesium, chioroisopropyi- (8);
Magnesium, chloro(l-methylethyl)- (9); (1068-55-9)
Zinc bromide (8,9); (7699-45-8)
2-(Phenylsulfonyl)tetrahydro-2H-pyran: 2H-Pyran, tetrahydro-2-(phenylsulfonyi)-
(11); (96754-03-9)
TRIS(TRIMETHYLSILYL)SILANE (Trisilane, 1,1,1,3,3,3-hexamethyl-2-(trimethylsilyl)-)
Me3SiCI + SiCI4 ---► (Me3Si)4Si
1. THF
(Me3Si)4Si + MeLi 2.h^/h2o (Me3Si)3SiH
Submitted by Joachim Dickhaut and Bernd Giese.1 Checked by George A. O'Doherty and Leo A. Paquette.
1. Procedure
Lithium powder (7.55 g, 1.07 moi) is placed in a 500-mL, four-necked flask equipped with a condenser, mechanical stirrer, dropping funnel, and low-temperature thermometer (Notes 1 and 2). The apparatus is carefully flushed several times with nitrogen followed by the addition of 50 mL of anhydrous tetrahydrofuran (THF). The reaction flask is cooled to approximately -60°C in a dry ice-acetone bath, and a mixture of freshly distilled (from CaH2> chlorotrimethylsilane (54.8 mL, 47.1 g, 0.43 mol) and tetrachlorosilane (Note 3) (10.1 mL, 15.0 g, 0.09 mol) in 140 mL of anhydrous THF is added over 1 hr by dropping funnel so that the temperature of the reaction mixture never exceeds -30°C. After addition is complete, stirring is continued for 0.5 hr with cooling (Note 4). The gold-brown suspension is allowed to warm to room temperature and stirred for 12 hr, during which time the color becomes more intense (Note 5). The thermometer is removed and the mixture is heated to reflux for 2 hr to destroy the remaining chlorotrimethylsilane. After the condenser is cooled to room
temperature, it is replaced with a nitrogen bubbler and gas inlet. Methyllithium-lithium bromide complex (66 mL, 99 mmol, 1.5 M in ether) is added over 3 hr to the grey-brown mixture with vigorous stirring (Note 6). During the addition a continuous stream of nitrogen is bubbled through the reaction mixture. After the reaction mixture is stirred for an additional 16 hr at room temperature, it acquires a greenish tint. Hydrolysis is carried out by the careful addition of the reaction mixture to 400 mL of ice-cold 2 N hydrochloric acid. [Caution: The solid residue may be highly pyrophoric. The checkers blanketed the flask with argon prior to the introduction of ether (100 mL) and poured the vigorously stirred slurry into the cold hydrochloric acid. This rinse procedure was repeated twice more.] The aqueous phase is extracted four times with 200-mL portions of pentane, the combined organic phases are dried over magnesium sulfate and the solvents removed under reduced pressure. Distillation under reduced pressure (1 mm, 38°C) affords 13.4-17.2 g of the product as a clear oil (60-77% yield).
2. Notes
1. The checkers used a three-necked flask having one arm equipped with a Claisen head.
2. All reagents were purchased from Fluka Chemical Corporation, except the methyllithium-lithium bromide complex, which was purchased from Aldrich Chemical Company, Inc., and were used without further purification. The lithium powder can be weighed in air; however, the use of a dust mask is recommended.
3. As tetrachlorosilane smokes strongly when exposed to air, introduction to the addition funnel is best carried out using a syringe.
4. If the temperature falls below -60°C, the mixture may solidify, but returns to a liquid upon warming.
5. The synthesis should be carried out over three days, stirring the mixture overnight. The stirring times reported should be considered a minicnum, and need not be followed exactly.
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