The Preparation and Reactivity of 2-Bromo-3-(tri-n-butylstannyl)-1-propene

Abstract

The preparation of 2-bromo-3-(tri-n-butylstannyl)-1-propene is described. This study characterizes the reactivity of 2-bromo-3-(tri-n-butylstannyl)-1-propene in S_E′ reactions with aldehydes and includes a survey of radical reactions of 2-bromo-3-(tri-n-butylstannyl)-1-propene with α-bromocarbonyl compounds for C-alkylation.

Key words

organostannane preparation - bifunctional reagent - S_E′ reactions - radical reaction - alkenyl bromides

• References and Notes

• 1 New address: A. A. Shah, Pfizer, Groton, CT, 06340, USA.
• 2 New address: D. A. Brooks, Eli Lilly & Company, Indianapolis, IN 46285, USA.
• 3 New address: N. Zorn, F. Hoffmann-La Roche AG, 4070 Basel, Switzerland.
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• 4b For an example of sequential cross coupling–carbocyclization reactions, see: Williams DR, Shah AA, Mazumder S, Baik M.-H. Chem. Sci. 2013; 4: 238

Two illustrative examples of total syntheses are cited:
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• 10c The data for the product 2-bromo-3-(tributylstannyl)prop-1-ene is given as follows: ¹H NMR (400 MHz, CDCl₃): δ = 5.6 (1 H, m), 5.35 (1 H, m), 2.25 (2 H, s), 1.70–0.70 (27 H, m). The reported data of their product differs substantially with respect to the key vinylic and allylic hydrogen assignments of Figure 1.
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For examples, see:
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• 17 The allylic alcohol 2-bromo-1-propen-3-ol (10.6 g, 64.3 mmol) was dissolved in CH₂Cl₂ at 0 °C, and Et₃N (10.3 mL, 73.9 mmol) was added under inert atmosphere. After stirring for 5 min, methanesulfonyl chloride (5.72 mL, 73.9 mL) was added dropwise at 0 °C. The reaction mixture was allowed to warm to 22 °C with continued stirring over 2 h. TLC (20% EtOAc in hexanes) shows the production of a less polar mesylate and the disappearance of starting alcohol. The reaction mixture was concentrated under reduced pressure to approximately one-third of its volume, and the concentrate was diluted with Et₂O (150 mL). The mixture was filtered through a pad of Celite^® to remove the triethylammonium hydrochloride precipitate with the aid of additional quantities of Et₂O. The filtrate was concentrated in vacuo to give the crude mesylate as a yellow oil with yields consistently in the 85–90% range. Vacuum distillation (1.4 mm Hg pressure) by Kugelrohr bulb-to-bulb transfer at an oven temperature of 60 °C afforded product as a colorless liquid which was judged to be >97% pure based on the ¹H NMR and ¹³C NMR spectra of these samples. ¹H NMR (400 MHz, CDCl₃): δ = 6.08 (1 H), 5.78 (1 H), 4.81 (2 H), 3.09 (3 H). ¹³C NMR (400 MHz, CDCl₃): δ = 124.1, 121.7, 72.3, 38.5). HRMS (CI): m/z calcd for C₄H₈BrO₃S [M + H]⁺ 214.9372; found: 214.9372. This mesylate was directly utilized in the next step.
• 18 Darwish A, Chong JM. Synth. Commun. 2004; 34: 1885