Steric influences in radical reactions. Part II. The abstraction of benzylic hydrogen atoms from 1-phenylphthalan, 1,3-diphenylphthalan, and 2-formyl-2′-methylbiphenyl by t-butoxy radicals

Abstract

Hydrogen-abstraction from 1-phenylphthalan by t-butoxy radicals at 120° liberates both of the radicals in which the free electron is at either of the benzylic carbon atoms C₃ and C₁, as evidenced by isolation of products resulting from rearrangement of the former radical and from dimerisation of the latter. Abstraction occurs from the methyl group of o-benzoyltoluene to give a radical which dimerises at 30°, but at 125° cyclises, to give ultimately anthraquinone and dianthrone. 1,3-Diphenylphthalan gives mainly 1,2-dibenzoylbenzene, the same product as when the phthalan is heated alone.

Abstraction from 2-formyl-2′-methylbiphenyl, at both 30 and 120°, occurs mainly at the aldehyde group; the benzoyl radical so formed then cyclises to 4-methylfluorenone in 60–67% yield. The intramolecular acylation of the radical is believed to be facilitated by steric effects.