t-Butyl 4-Benzoylperbenzoate

[71616-77-8]  · C18H18O4  · t-Butyl 4-Benzoylperbenzoate  · (MW 298.34)

(reagent for low-temperature initiation of radical reactions)

Physical Data: mp 62-64 °C.

Solubility: sol benzene, methanol, cyclohexane.

Form Supplied in: not commercially available.

Preparative Method: prepared from the corresponding carboxylic acid chloride by treatment with t-Butyl Hydroperoxide.1

Handling, Storage, and Precautions: avoid exposure of the reagent to light and heat; store protected from light in a refrigerator or freezer.

In the search for efficient photoinitiators for polymerization processes and radical C-C bond forming reactions a range of novel peresters were prepared, including t-butyl 4-benzoylperbenzoate (1).1 On photolysis this compound undergoes efficient homolysis of the peroxide linkage, producing a carboxyl radical and a t-butoxy radical (eq 1). The latter is able to initiate further radical chemistry by hydrogen atom abstraction from a suitable donor. The advantages of using this system are that radical chemistry can be initiated at relatively low temperatures (contrasting with the thermal conditions often employed, such as Azobisisobutyronitrile in benzene at reflux) and the irradiation is carried out at relatively long wavelength (360 nm) which should not cause unwanted excitation in most other reactants.

The use of this initiator has been examined in some Kharasch-type additions of acyl radicals to alkene acceptors (eqs 2 and 3).2

In competition reactions, involving addition to either 1-hexene or methyl crotonate, addition to methyl crotonate is preferred with the highest selectivity being observed when the reaction was conducted at 4 °C. This selectivity was then utilized to effect a cyclization reaction (eq 4).

Of the two possible pathways, only that resulting in the six-membered ring product is observed, due to the high regioselectivity in the initial acyl radical addition. Alternative methods of initiation of the reaction, using Dibenzoyl Peroxide or photolysis in the presence of benzophenone, were tried for comparison, but gave markedly lower yields of product.

1. Thijs, L.; Gupta, S. N.; Neckers, D. C. JOC 1979, 44, 4123.
2. Gottschalk, P.; Neckers, D. C. JOC 1985, 50, 3498.

Nigel S. Simpkins

University of Nottingham, UK

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