ABSTRACT
For the first time through quantum chemistry methods, the effective use of 1JCLi spin-spin coupling constants as descriptors for assessing the formation of strained metallacycles is demonstrated. Both acyclic organolithiums and 3- to 7-membered metallacycles are examined. 80 organolithium compounds, including both monomeric and dimeric species, with ligands containing fluorine, nitrogen, oxygen, and carbon (in the form of carbanions), are tested. In general, the 1JCLi values below 12 Hz for monomeric species and below 6 Hz for dimeric species serve as clear indicators of strained monomeric metallacycle formation (for 6Li nuclei). The primary contributor to the overall 1JCLi value is the Fermi-contact term, which correlates directly with the carbon-lithium interatomic distance and allows to distinguish between dimers and monomers.
ABSTRACT
A simple and effective organolithium approach to the synthesis of 2-substituted benzo[cd]indoles from peri-dihalonaphthalenes and nitriles has been developed. The reaction proceeds via a surprisingly easy intramolecular aromatic nucleophilic substitution facilitated by the "clothespin effect". The discovered transformation provides good isolated yields, allows usage of an extensive range of nitriles, and demonstrates a good substituents tolerance. UV-absorption and NMR spectra of the obtained benzo[cd]indoles and their protonated forms demonstrated exclusive protonation to the indole nitrogen atom even in the presence of two NMe2 groups in positions 5 and 6 (i. e. "proton sponge" moiety).
ABSTRACT
The tetrazole cycle is a well-known pharmacophore fragment that is part of the structure of a large number of biologically active compounds, including drugs. The diverse biological properties of such heterocylic systems and related compounds are largely determined by their ability to form strong hydrogen bonds with the targets. However, quantitative data on the hydrogen bonding of such heterocycles are limited. In the present article, we have determined the hydrogen bonding basicity constants (pKHB) of a series of 2-substituted-2H-tetrazoles as well as of some 1,5-disubstituted-1H-tetrazoles, 1H-triazoles in 1,1,2,2-tetrachloroethylene by means of FTIR spectroscopy. The influence of the nature of the substituents on the pKHB values of these compounds has been evaluated. Also, the structure of the HB complexes and the theoretically predicted pKHB values have been discussed by means of the DFT approach using the B3LYP/6-311++G(d,p) basis set and CPCM model. It was shown that in the case of 2,5-disubstituted-2H-tetrazoles, the endocyclic nitrogen atom at position 4 is the most preferred basicity center. Thermodynamic parameters of the hydrogen bonding complex formation have been also determined experimentally and calculated by the theoretical method.
