Intermolecular alkyl radical addition to pentafluorophenyl vinylsulfonate.; 3,3-Dimethyl-butane-1-sulfonic acid pentafluorophenyl ester

Jonathan Wilden ([email protected]),
A contribution from the Caddick Group, Sussex

Chemicals Used
Pentafluorophenyl vinylsulfonate (250 mg, 0.91 mmol) Distilled toluene (15 mL) AIBN (10 mg, Acros) 2-Iodo-2-methylpropane(3.0 eq., 0.50 g, 2.7 mmol, Lancaster) Tributyltin hydride (2.5 eq., 0.66 g, 2.3 mmol, Lancaster) Potassium fluoride (ca. 1.5 g, Avocado)

Procedure
To a solution of the vinylsulfonate (250 mg, 0.91 mmol) in dry toluene (15 mL) was added AIBN (10 mg), and 2-iodo-2-methylpropane(3.0 eq., 0.50 g, 2.7 mmol) and the solution heated to 100 °C. Tributyltin hydride (2.5 eq., 0.66 g, 2.3 mmol) was added dropwise over 20 mins and the reaction allowed to heat for a further 2h. Potassium fluoride (ca. 1.5 g) was added and the resulting suspension stirred vigorously for 16h. The suspension was filtered through celite and the filtrate concentrated in vacuo. The crude product was purified by flash column chromatography (20-50% Ether / Petroleum ether 40-60 °C) to yield the product as a pale yellow, oil (257 mg, 0.77 mmol, 85%).

Author's Comments
The reaction is pretty reliable on scales from 100 mg to 1 g. Most simple alkyl radicals work well although yields for primary halides are generaly a little lower (typically around 65%). The work-up procedure allows the removal of excess tributyltin iodide which is otherwise very difficult to remove by column chromatography.

Data
¹H NMR (300 MHz, CDCl₃)3.50-3.30 (2H, m, SO₂CH₂), 1.88-2.00 (2H, m, SO₂CH₂CH₂), 0.96 (9H, s, (CH₃)₃).

Lead Reference
Caddick, S.; Wilden, J. D.; Bush, H. D.; Wadman, S. N.; Judd, D. B.; Org. Lett.; 2002; 4(15); 2549-2551.

Other References

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