Checked by Bruce M. Branan and Leo A. Paquette.
1. Procedure
A dry,
500-mL, three-necked flask appropriately shaped to accommodate the horn of an ultrasonic processor is equipped with a
thermometer and a
pressure-equalizing dropping funnel to which a
nitrogen inlet is attached. A
nitrogen atmosphere is established in the flask, which is charged with
100 mL of anhydrous tetrahydrofuran (THF) (Note
1),
3.04 g (0.125 mol) of magnesium (Mg) turnings (Note
2),
32.5 g (0.100 mol) of tributyltin chloride (Note
2), and a small piece of
iodine (optional), and then immersed in an
ice-salt bath. After the temperature of the solution falls below 15°C,
13.4 mL (0.120 mol) of 1-chloro-3-methyl-2-butene (Note
3) in
50 mL of THF is added dropwise over 30–60 min while maintaining the temperature at less than 20°C (Note
4) under sonication at an output power of 30–75W (Note
5). After the addition is complete, sonication is continued for a further 30–45 min (Note
6) to complete the reaction. The reaction mixture is poured into 400 g of ice water and the mixture is extracted with three
100-mL portions of ether. The combined ethereal solutions are washed with 50 mL of water and
50 mL of brine, dried over anhydrous
magnesium sulfate, and evaporated under aspirator pressure to yield a colorless oil. This oil is further evacuated (1 mm) at room temperature for 1 hr (Note
7) to give
36 g (
100%) of
tributyl(3-methyl-2-butenyl)tin. This material is sufficiently pure for direct use in most reactions, but can be purified by distillation to afford
33.2 g (
92%) of colorless oil, bp
105–107°C (0.01 mm) (Note
8),(Note
9),(Note
10).
2. Notes
2.
Magnesium turnings were purchased from Wako Pure Chemical Industries and the Aldrich Chemical Company, Inc.
Tributyltin chloride was obtained from Tokyo Kasei Kogyo and the Aldrich Chemical Company, Inc. They were used without further purification.
4. The reaction temperature should be kept below 20°C to prevent side reactions. If the temperature exceeds 20°C, one should stop both the addition of the
prenyl chloride and the ultrasound irradiation, and wait for the reaction temperature to fall below 15°C.
5. The submitters used
Heat Systems-Ultrasonics Model W-220 (maximum output power 200W) with a standard horn. The checkers used a
Sonics and Materials Inc. Vibra-Cell High Intensity Ultrasonic Processor (maximum power outlet 600W) fitted with a 13-in extender probe. If the applied ultrasonic processor does not have a power meter, one can judge the applied power by the occurrence of vigorous stirring of the
Mg turnings around the immersed ultrasonic horn. If the
Mg turnings settle to the bottom of the flask, the applied sonication power is insufficient.
For reaction on a 10-mmol scale, an ultrasonic cleaner with sufficient output power (e.g., Branson Model B-220) can be used for external irradiation.
6. After completion of the reaction, ultrasonic irradiation for an unnecessarily long period causes decomposition of the allyltributyltin. The end of the reaction can be determined by a faint turbidity in the solution and by darkening of the brilliant Mg surface.
7. Through this treatment, most of the low-boiling impurity can be removed.
8. Good purity (95–98%) is observed by GLC (
glass capillary column, OV-101, 0.33 mm × 25 m) at an
oven temperature of 200°C.
9. Because of modest thermal instability of the material, one should distill at a bath temperature below 150°C. When the bath temperature exceeds 150°C, considerable decomposition of the allylic
tributyltin occurs and a poorer yield is realized. The checkers measured a bp of 100°C at 0.1 mm.
10. The spectrum is as follows:
1H NMR (400 MHz, CDCl
3) δ: 0.83 (m, 6 H, SnCH
2), 0.89 (t, 9 H, J = 7, CH
3 of Bu), 1.29 (m, 6 H, SnCH
2CH
2), 1.47 (m, 6 H, CH
2CH
3), 1.57 (s, 3 H, cis-CH
3), 1.64 (d, 2 H, J = 9, CH
2CH=C), 1.67 (s, 3 H, trans-CH
3), 5.28 (broad t, 1 H, J = 9, CH=C);
13C NMR (75 MHz, CDCl
3) δ: 9.4, 10.7, 13.7, 17.4, 25.5, 27.4, 29.3, 123.0, 125.3;
119Sn NMR (120 MHz, CDCl
3) δ: −13.4.
All toxic materials were disposed of in accordance with "Prudent Practices in the Laboratory"; National Academy Press; Washington, DC, 1995.
3. Discussion
This procedure describes ultrasound-promoted Barbier-type cross coupling of an allylic chloride with
tributyltin chloride.
2 Allylic trialkyltin derivatives have also been prepared by (i) a coupling reaction of a trialkyltin chloride with an allyl Grignard reagent
3,4,5 or allyllithium,
6,7 and allyl derivatives with stannyl metals,
8,9,10,11,12 (ii) stannylation of allylic sulfides,
12 sulfones,
13,14 selenoxides,
15 alcohols,
16 and allyl palladium.
17,18,19 The method with an allylic Grignard reagent prepared in advance of the coupling reaction is an alternative to this method, but the ultrasonic procedure is more convenient and effective. For the preparation of simple allyltributyltin or its homologues, the present method has advantages over other methods, especially because of easy manipulation and scale-up, reproducibility, and yield.
This procedure is representative of a general and versatile method for the preparation of allylic tributyltins. Other allylstannanes prepared using this method are shown in the Table.
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