Synthesis,Characterization, and Computational Studies of Selenium Derivatives of 3,5‐Dichloropyridine

A methodology that can be tailored to incorporate selenium at the C‐2 or C‐4 position of 3,5‐dichloropyridine ( 1 ) was developed. For this, the lithiation of 1 with and without prior boron trifluoride complexation was utilized. The use of 1.3 equiv of LDA in the reaction did not give the desired product; however, the use of 2.3 equiv of LDA successfully inserted selenium into the C─Li bond. The observed regioselectivity in these reactions has been explained in light of relative stability of the lithiated species formed in dimethyl ether solution. Quantum chemical analysis was used to calculate the deprotonation energy and pK _a values and correlated with the observed regioselectivity. Theoretical analysis (B3LYP/6‐311++G(d,p)) of the synthesized compounds was performed to predict the effect of structural variations on the molecular properties of pyridylselenium derivatives. Various thermodynamic parameters and HOMO‐LUMO energies in the gas and solvent phases were calculated. When compared with 1 , the insertion of selenium into a pyridine moiety drastically reduces the HOMO‐LUMO energy gap, which clearly explains photochemical liability of selenium‐containing pyridine derivatives. The ¹H‐ and ¹³C‐NMR chemical shifts were also calculated by using gauge‐including atomic orbital method, and the results were validated with the experimental data.