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.