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P:;ridyl ketones react with low valent titanium reagents, generated either by LiAlH4 and TiC13 or NaO and TiC13, to give either the corresponding alcohol or the reductively coupled products. The olefinic products generally arise when intramolecular N-complexation of the titanium ions is prevented, and ill-defined polymeric material is formed when two sites of potential complexation are available.Recently, intermolecular reductive coupling of aldehydes and ketones to olefins has been accomplished by the use of low valent titanium reagents which were generated from titanium trichloride with either lithium aluminum hydride2 or a reactive metal,3 such as Zn, Mg, or Li. In general to the best of our knowledge, all cases of reductive coupling, via this procedure, have been limited to aromatic or aliphatic ketones and aldehydes; few, if any, heterocyclic carbonyl compounds have been utilized. We herein report the reaction of pyridyl ketones with low valent titanium reagents.Both tetraphenyletheneZa and bis(fluorenylidene)2a have been successfully prepared in our hands from the corresponding ketones in excess of 85% yield by either method a (LiAlH4-TiC13 P a or b (NaD-TiC1:j).3 Treatment of phenyl 2-pyridyl ketone ( l a ) under method a conditions afforded (93%) phenyl(2-pyridyl)methanol(2a) and, in low yields (ca. 5%), the reduced coupled compound 3a. The mass spectral l a , Ar = C,H, 2 b, Ar = 2-pyr 3 data of 3a indicated a weak parent ion (mle 336; 28%) and formation of a very intense mle 168 peak ( C~~H~O N , lOoO/o) due to the facile fragmentation of the central bis(benzy1ic) bond.NMR spectral data of 3a showed a singlet at 6 5.31 for the nonexchangeable benLylic hydrogens and a complex aromatic region, which i; not indicative of the expected rigid tetrasubstituted ethenes. Di-2-pyridyl ketone ( l b ) similarly gave the corresponding alcohol Zb, which upon prolonged contact with air underwent easy oxidation to both starting l b and several minor uncharacterized products. Reduction, via method b, of l b afforded only the carbonyl reduced product 2b along with unchanged starting material.3-Benzoylpyridine (4), when treated with TiC13-LiAlH4 in T H F (method : I ) , gave the desired isomeric coupled olefins ( E ) -5 and (Z)-5 as well as unchanged starting material. Mass spectral data for 5 showed an intense parent ion (mle 334, 100%) and both possessed near superimposible fragmentation patterns. The NMR spectral data of (2)-5 and (E)-5 indicated the unique 2,6-pyridyl hydrogens, an upfield shift of the ophenyl hydrogen (compared to 4), and a complex aromatic ( Z 1-5 ( E ) -5 region. Eu-shift studies were conducted on both isomers in order to ascertain their configurations (Figures 1 and 2). At 21% Eu-shift reagent [Eu(fod)~], the 5-ppm downfield shift of the 2,6-pyridyl hydrogens confirmed that the shift reagent is complexed with the pyridyl nitrogen atom(s). The near first-order spectrum and decoupling experiments indicated that the 199-200 "C melting isomer possesses the Z configuration.

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The syntheses of l,2-bis(3-methylphenyl)-, l-(6-methyl-2-pyridyl)-2-(3-methylphenyl)-, and l,2-bis(6methyl-2-pyridyl)benzenes are described. The aryl and heteroaryl olefins were brominated and didehydrobrominated to give the corresponding acetylenes, which were treated with -pyrone to generate the respective ortho-substituted benzenes. The methyl substituents were oxidized with potassium permanganate to give, after esterification, the diesters. l,2-Bis(6-methyl-2-pyridyl)benzene was -brominated and cyclized with sodium sulfide to give the thiacyclophane 25. The barrier for ring inversion of 25 was ascertained by VT NMR to be AG* = 12.5 kcal/mol at 245 K. Attempts to determine the rotational barriers of 11 and 12 were unsuccessful; however, a AG* of 10 kcal/mol was estimated for 13.