Chlorination and Bromination of 1-Phenanthrol -Aromatic Halogenation at Crowded Positiont-

Abstract

With interest in the substitution reaction at a crowded position, the halogenation of 1- phenanthrol [1] was studied. The chlorination of [1] with SO₂Cl2 in AcOH afforded the 4-chloro [4] and 2, 4-dichloro compound [5] successively. On the bromination with Br₂ (1 mol) in CCl₄, [1] gave the 2-bromo compound [2], while in the presence of Na₂CO₃ it gave mainly the 4( ? ) -bromo isomer [3] When contacted with an acid, [3] isomerized to [2] with great ease, and because of this lability it was not purely isolated. From these facts the course of the bromination is assumed as follows:
The methyl ether of [2] was treated with n-butyllithium and dry-ice successively to yield the corresponding 2-carboxylic acid [7]. This acid was converted by the Curtius reaction into 1-methoxy-2-phenanthrylamine, which was also derived from an authentic 1-methoxy-2- nitrophenanthrene. The oxidation of [4] with CrO₃ gave 1, 4-phenanthrenequinone.
The high reactivity of the crowded 4-position in the chlorination was assumed to be due to steric acceleration in the addition-step.