t-Butyl acetate as a t-butyl cation equivalent: O-Alkylation of N-Hydroxyphthalimide; t-butoxyphthalimide

Andrew McCarroll (kafy3@sussex.ac.uk),
A contribution from the Walton Group, St. Andrews

Chemicals Used
1,4-dioxane (300 ml), t-butyl acetate (75 ml; 0.56 mol), N-hydroxyphthalimide (8.15 g; 0.05 mol), 72% perchloric acid (0.5 ml).

Procedure
The reagents are mixed together (in order listed), and stirred in a stoppered flask for 24 hours at room temperature. Saturated aqueous sodium bicarbonate solution is added until there is no more effervescence (~200 ml). The organic layer is separated, and concentrated. The crystals are dissolved in ether, dried and concentrated, then recrystallised (40/60 Petrol). Yield: 8.81 g; 80%.

Author's Comments
The reference that the procedure was taken from (see below) was in Russian, and our translation indicated that the dioxane layer should be extracted with DCM, but the solvents were miscible, so the method described was used. A first attempt, in which the mixture turned blood-red, failed for unknown reasons and the successful attempt seemingly followed the same procedure. The technique was used because the usual way to prepare N-alkoxyphthalimides, Mitsonobu condensation ([SyntheticPage 122] ), failed.

Data
m.p. 110.5-113 ^oC. (lit 110-111 ^oC; Chimiak and Kolasa)¹H nmr (300 MHz, CDCl₃) 1.43 (9H,s), 7.65-7.85 (4H, ArH)

Lead Reference
A. J. McCarroll and J. C. Walton, J. Chem. Soc. Perkin Trans. 2, 2000, 1868.

Other References
A. Chimiak, T. Kolasa. Rocz. Chem., 1974, 48, 139. t-Butyl acetate is reported to be a good general t-butylating agent in the presence of a strong acid. E. Taschner, Cz. Wasielewski, J. F. Biernat, Ann., 1961, 646, 119.

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