Synthetic studies in the biphenyl series

Abstract

2,2'-Di(l-hydroxy-l-methylethyl)biphenyl has been prepared in poor yield from 2,2'-dilithiobiphenyl and acetone. Attempts to resolve it or to activate it optically have failed. The use of the Wittig olefin synthesis in the biphenyl series has been studied. 2,2'-Bis(triphenylphosphoniomethyl)biphenyldibromide has been prepared in a pure state and converted into the corresponding phosphorane by the action of n-butyllithium.The phosphorane, although not isolated, reacts readily with aldehydes but has failed to react with the ketones acetone and cyclohexanone, indicating that it is rather stable. With benzaldehyde, the phosphorane condenses to give 2,2'-distyrylbi-phenyl wich, on hydrogenation for different periods of time, gives 2,2'-diphenethylbiphenyl and 2,2'-bis([beta]-cyclohexylethyl) biphenyl. The geometrical structure of 2,2'-distyrylbiphenyl was discussed as an alternative approach carbomethoxymethylenetriphenyl-phosphorane has been treated with carbonyl compounds in the biphenyl series. It fails to react with ketones under ordinary conditions (confirming the recently published findings of Trippett and Walker) but reacts readily with aldehydes. From its condensation with biphenyl-2,2'-dialdehyde, prepared by an improved route from phenanthraquinone, two isomeric 2,2'-bis ([beta]-carbomethoxyvinylene)biphenyls have been obtained, and their stereochemistry is discussed. Attempts to synthesise 2,2'-bridged biphenyls with 8- or 9-membered bridging rings by the reaction of biphenyl-2,2'-dialde-hyde with Wittig reagents from ethylenebis(triphenylphosphonium) dibromide and trimethylene-1,3-bis(triphenylphosphonium) dibromide have been unsuccessful. Heterocyclic bridged compounds have been obtained from the condensation of the dialdehyde with o-phenylenediamine but the exact structure of the products is still uncertain. From the condensation of ethyl 3,4-diamino-benzoate with the dialdehyde, 3"-carbethoxy-5,10-dihydro-2,3:6,7: 8,9-tribenzo-1,4-diazecine has been obtained. If this condensation is carried out at room temperature, and not at 150[degrees], 3"-carbethoxy-phenanthrene-9',10' :.2,3-quinoxaline is obtained as a by-product. It has not so far proved possible to demonstrate optical activity in either 2,2'-bis(triphenylphosphoniomethyl)biphenyl dibromide or in its 6-nitro derivative, although steric hindrance to rotation round the 1,1'-bond in the latter compound must be considerable.