Inga Cikotiene

An oxocarbenium ion mediated cyclization of (Z)-1,3-diarylprop-2-yn-1-one O-methyloximes and 3-arylprop-2-yn-1-(2-methoxyphenyl)-1-ones resulted in regioselective formation of functionalized isoxazoles and chromones, respectively. Alkoxy(aryl)methyl group containing compounds were obtained in good and high yields.

Cyclopropyl‐tethered 3‐alkynyl imines react with polarized‐covalent‐bond‐containing compounds to give polyfunctionalized pyrroles. This provides a mild and effective method for the simultaneous introduction of halogen, chalcogen, or hydrogen groups to the 3‐position of the pyrrole ring, together with the incorporation of halogen, azide, or alkoxy/aryloxy groups into the ethyl side‐chain.

Metal‐free halogen, chalcogen, or oxocarbenium ion mediated yne‐carbonyl or yne‐thioxo transformations of a range of N‐ and O‐propargylic compounds have been studied. This investigation has led to the development of a mild, economic, and effective method for the synthesis of functionalized 4H‐1,3‐oxazines, 4H‐1,3‐thiazines, 4,5‐dihydrothiazoles, and α‐substituted enones. The structure of the propargylic substrate and the nature of electrophile influence both the outcome and regioselectivity of processes.

Electrophilic cyclization of N-(3-arylprop-2-ynyl)amides to functionalized 4H-1,3-oxazines is described. It was found that the presence of an electron-rich aryl group next to the triple bond is crucial for a smooth and highly regioselective 6-endo-dig ring closure process.

Mechanistic studies of the reaction between 3‐arylprop‐2‐ynyl esters and aldehydes catalyzed by BF₃⋅Et₂O were performed by isotopic labeling experiments and quantum chemical calculations. The reactions are shown to proceed by either a classical alkyne–carbonyl metathesis route or an unprecedented addition–rearrangement cascade. Depending on the structure of the starting materials and the reaction conditions, the products of these reactions can be Morita–Baylis–Hillman (MBH) adducts that are unavailable by traditional MBH reactions or E‐ and Z‐α,β‐unsaturated ketones. ¹⁸O‐Labeling studies suggested the existence of two different reaction pathways to the products. These pathways were further examined by quantum chemical calculations that employed the DFT(wB97XD)/6‐311+G(2d,p) method, together with the conductor‐like screening model for realistic solvation (COSMO‐RS). By using the wB97XD functional, the accuracy of the computed data is estimated to be 1–2 kcal mol⁻¹, shown by the careful benchmarking of various DFT functionals against coupled cluster calculations at the CCSD(T)/aug‐cc‐pVTZ level of theory. Indeed, most of the experimental data were reproduced and explained by theory and it was convincingly shown that the branching point between the two distinct mechanisms is the formation of the first intermediate on the reaction pathway: either the four‐membered oxete or the six‐membered zwitterion. The deep mechanistic understanding of these reactions opens new synthetic avenues to chemically and biologically important α,β‐unsaturated ketones.

A N-nitroso moiety can be used for the activation of chloropyrimidines toward a nucleophilic substitution reaction with amines. The subsequent treatment of the obtained products with aq H₂SO₄ can lead to either N-denitrosation to obtain 4,6-pyrimidinediamines or to a Fischer–Hepp type rearrangement to obtain 5-nitroso-4,6-pyrimidinediamines. It was found that the outcome of the reaction strongly depends on the structure of the pyrimidines. Activation of the pyrimidine ring by three groups with a positive mesomeric effect is crucial for the intramolecular nitroso group migration.

An N-nitroso group was used to activate chloropyrimidines toward nucleophilic substitution by amines. This permitted a simple, one-pot, high-yielding synthesis of pyrimidine-4,6- and -2,4-diamines.