10259-15-1

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The reaction of lithium aluminium hydride (LAH) and pyridine yields five lithium tetrakis(N-dihydropyridyl)aluminate (LDPA) isomers.The LDPA isomers are formed reversibly and contain both 1,2- and 1,4-dihydropyridyl ligands.The 1,2-dihydropyridyl ligands are incorporated as the products of kinetic control while the 1,4-dihydropyridyl ligands are formed as the thermodynamic products.When LDPA is synthesized using lithium aluminium deuteride and the deuterated LDPA is placed in pyridine solvent, the ligands exchange with the pyridine in the solvent pool and form pyridine which is deuterated mainly in the 2- and 4-position.A small amount of 3-deuterated pyridine is also detected.The formation of 3-deuteriopyridine suggests that the pyridine radical anion is an intermediate present during the reaction of LAH with pyridine.In support of this suggestion, when LAH and pyridine are mixed, the EPR spectrum of the lithium salt of the pyridyl radical anion is observed.The stepwise addition of ligands to form LDPA is observed (NMR).Five aluminate species are detectable (27Al NMR): LAH , mono-, di-, and -trisubstituted aluminium hydride, and LDPA.The hydrolysis of LDPA in solvent pyridine-d5 yields a mixture of 1,4-, 1,2-, and 2,5-dihydropyridines.The dihydropyridines are stable in the absence of oxygen.

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Pyridine N-oxide and the monodeuterated species have been prepared and their microwave spectra investigated for J-values up to 10.The complete rs structure is determined from these data combined with data from earlier measurements on the 13C- and the 15N-substituted species .The N-O bond length obtained here is intermediate between the typical single and double bond length found in other gas phase molecular structures.The structure of the C-N-C part of pyridine N-oxide is found to be significantly different from the corresponding part of the pyridine structure.

Secondary isotope effects (IEs) on basicities of various deuterated pyridine isotopologues and of 2,6-lutidine-2,6-(CD3)2 have been accurately measured in aqueous solution by an NMR titration method applicable to a mixture. Deuteration at any position of pyridine increases the basicity, but the IE per deuterium is largest for substitution at the 3-position and smallest for the 2-position, which is closest to the site of N-protonation, smaller even than that for 2-CD3 substitution. Computations at the B3LYP/cc-pVTZ level overestimate the magnitude of the measured IEs but largely reproduce the variability with isotopic position. Because the calculated IEs are based on changes in vibrational frequencies on N-protonation, the correspondence between calculated and experimental IEs implies that they arise from zero-point energies, rather than from inductive effects.

The isolation of mixtures of 2-, 3-, and 4-deuteriopyridine, 2-, 3-, and 4-trimethylsilylpyridine, or 2-, 3-, and 4-methylthiopyridine indicates successful metallation of pyridine with a 1:1 mixture of BuLi-ButOK in tetrahydrofuran-hexane at -100 deg C.

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Precise deuterium incorporation with controllable deuterated sites is extremely desirable. Here, a facile and efficient electrocatalytic deuterodehalogenation of halides using D2O as the deuteration reagent and copper nanowire arrays (Cu NWAs) electrochemically formed in situ as the cathode was demonstrated. A cross-coupling of carbon and deuterium free radicals might be involved for this ipso-selective deuteration. This method exhibited excellent chemoselectivity and high compatibility with the easily reducible functional groups (C=C, C≡C, C=O, C=N, C≡N). The C?H to C?D transformations were achieved with high yields and deuterium ratios through a one-pot halogenation–deuterodehalogenation process. Efficient deuteration of less-active bromide substrates, specific deuterium incorporation into top-selling pharmaceuticals, and oxidant-free paired anodic synthesis of high-value chemicals with low energy input highlighted the potential practicality.