3,3 -Dimethyl-2,2 -biquinoline, formation

Photodehydrogenation reactions may lead to dimerization or cycli-zation. Intermolecular dehydrogenation with ultraviolet light has been recently illustrated in the formation of 2,2 - bipyridine, 6,6 -dimethyl-2,2 -bipyridine, and 2,2 -biquinoline on irradiation of pyridine, a-pico-line, and quinoline, respectively, under nitrogen in cooled quartz tubes.216... 

The formation of five-coordinate gold(III) has been demonstrated clearly in the complexes of 2,9-dimethyl-l,10-phenanthroline and 2,2 -biquinoline, which have the distorted square pyramidal structures (91) and (92). However, the structures of the ligands prevent square planar coordination, so that these examples are atypical.613-615 However, a related organometallic derivative, [AuCl(C4Ph4)(phen)], is known and has a similar distorted square pyramidal structure.616... 

The relatively vigorous reaction conditions required to effect vinyl substitution by heteroaryl halides under the influence of Pd-catalysis may lead to homo-coupling. The dominating reaction path in attempted alkenyl-ations of 4-iodopyrimidines was the formation of 4,4 -bipyrimidines (19) (Scheme 4 Section II.A.2). In reactions of 4-iodopyrimidines with a Pd-catalyst at 160°C, near-quantitative yields of the 4,4 -bipyrimidine were obtained (79CPB193). Also, in the reaction of 2-iodo-4-methylquinoline with Pd(OAc)2 as added catalyst, a major reaction path led to 4,4 -dimethyl-2,2 -biquinoline (Scheme 2 Section II.A.2.) (82CPB3647). 

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