Hydrogen bonding-assisted transformations of cyclic chalcones: <i>E/Z</i>-isomerization, self-association and unusual tautomerism

Abstract

Condensation of 1- or 2-indanones and 1,3-indandiones with aromatic or heteroaromatic carbaldehydes gives products that demonstrate various transformations and effects of general interest for organic chemistry. In the present review, phenomena such as tautomerism, E/Z-isomerization, π-conjugation, hydrogen bonding, and homo- and heteroassociation are considered. The relative stability of various isomers of cyclic chalcones is shown to be determined by the intramolecular hydrogen bonding in their molecules and the formation of associates. The same effects also result in the formation of unusual, otherwise unstable tautomers, such as 2H-indazoles. The hydrogen bonding-assisted keto-enol and E/Z-isomerization are analyzed. A novel, specific type of conjugation for the studied compounds was proposed and termed "roundabout" conjugation. The bibliography includes 101 references.

Unusual spontaneous oxidation of 2,2′‐(quinolin‐2‐ylmethylene)bis(1H‐indene‐1,3(2H)‐dione): An experimental and theoretical study of the mechanism

“…FTIR and UV-vis spectra of compound 7 were recorded in CH 2 Cl 2 solutions. All quantum-chemical calculations were performed at the DFT level with B3LYP potential, which was successfully used in numerous studies including our previous works on the related systems (e.g., previous studies [3,7,11] ). The 6-311G(d,p) basis set was augmented with diffuse d functions on heavy atoms and diffuse p functions on hydrogen atoms because of their importance for molecules with lone pairs, as in the studied molecules.…”

“…The reaction of 1,3-indandione 1 with hetarylcarbaldehydes is a convenient route to various compounds, which are of interest both from theoretical point of view and in the perspective of their application as photoswitches, [1] semiconductors and photosemiconductors, [2] sensors for anions, [3] precursors for the synthesis of drugs and dyes, and so forth. [4][5][6] Our systematic studies summarized in a recent review [7] showed that the molecules combining in their structure nitrogen-containing aromatic heterocycles and 1,3-diketones or cyclic chalcones are subject to a large variety of dynamic processes, including the formation and cleavage of hydrogen bonds, proton transfer, reversible Z/E isomerization, and tautomeric and rotameric transformations. The reaction of 1,3-indandione with aldehydes proceeds via the intermediate adducts 2, which either undergo dehydrogenation with the formation of the products of condensation 3 or react with the second molecule of 1 forming the 1:2 adducts 4 (Scheme 1).…”

Complexes on the Base of a Proton Transfer Capable Pyrimidine Derivative: How Protonation and Deprotonation Switch Emission Mechanisms

“…Proton transfer processes, including inter- and intramolecular, belong to the most important chemical reactions. − Molecules of organic and coordination compounds featuring short intramolecular O–H···N and O–H···O hydrogen bonds between adjacent aromatic/heteroaromatic groups can undergo intramolecular proton transfer processes. ,− The excitation of such molecules with light makes the O–H group more acidic and the proton acceptor atom, N or O, more basic as a result of the redistribution of electron density between the electron-donating and electron-withdrawing groups. This shift of electron density triggers the reaction referred to as excited state intramolecular proton transfer (ESIPT) in which the proton is transferred to the proton acceptor atom, and the molecule is converted from its normal form (i.e., the most stable in the ground state) to the tautomeric form (Scheme ).…”