Synthetic studies in bridged biphenyls

Abstract

The reaction between 2,2'-bisbromomethylbiphenyl and tri-phenylphosphine has been found to produce a mixture of the monoand di-phosphonium bromides. The effects involved in the practical work together with the difficulty in separating the mixture seemed to indicate that a pure di-phosphonium bromide, the 2,2'-bis(tri-phenylphosphoniomethyl)biphenyl dibromide, could not be obtained by the various methods described in the experimental section. Attempts to prepare a 2,2'-bridged biphenyl with a larger bridging chain by the reaction between biphenyl-2, 2'-dialdehyde and a P(0)-activated reagent such as trimethylene-bis(diphenylphosphine oxide) have been unsuccessful.A nine-membered ring, the 1-methyl-2,3,8,9-tetrahydro-4,5:6,7-dibenzazonine (m.p. 55-56°) has been synthesized and optically activated by crystallization of its camphorsulphonate (m.p. 201-202°) from acetone. The base liberated from this salt was found to have chloroform, to be optically stable at room temperature and to undergo complete racemization on heating under reflux in cyclohexane for one hour. Its ultra-violet spectrum also reflects a large angle of torsion in the ground state, comparable with that of the 1, 2, 3,4-dibenzcyclonona-1, 3-diene-7-carboxylic acid. Besides the camphorsulphonate, the methiodide, the picrate and the tartrate of this compound have all been prepared and characterized.A reinvestigation of a series of condensation reactions between biphenyl-2,2'-dialdehyde and several diamines is also included in the present work. The condensation between 2,2'-diaminobiphenyl and o-phthalaldehyde has been found to give a red crystalline solid (m.p. 253-254°) as a main product. Spectroscopic studies seem to show that it could not be the cis 10[N-(2"-amino-2' -biphenylyl) 1-isoindol-3-onylidene]isoindolo[2.1-a ] dibenzo [d.f]-1,3-diazepine as proposed by Bindra and Elix. A possible structure for this red compound has been tentatively advanced but some of its chemical reactions require further study.