Dmitrii A. Shabalin

A convenient synthesis of spiro-fused cyclohexadienones/pyrrolizines from pyrrolyl ynones and p-quinone methides through a base-catalyzed 1,6-conjugate addition/ipso-cyclization tandem reaction is described. The protocols feature good substrate tolerance, mild reaction conditions, and high yields of target products. The problem of reaction stereoselectivity raised during the scope study is easily solved by employing a one-pot, two-step approach that allows directing the reaction sequence to obtain the desired products exclusively with the (Z)-configuration of the enone moiety. A tentative reaction mechanism is proposed with the support of experimental studies.

A convenient, catalyst‐free protocol for the synthesis of hitherto unknown alkyne‐tethered N ‐acyl pyrazolines from readily available hydrazides and skipped diynones has been developed. The subsequent acid‐catalyzed dehydration of the synthesized hydroxy derivatives opened a shortcut toward a representative set of 5‐alkynyl‐1‐acylpyrazoles. The elaborated approaches possess competitive advantages such as complete chemo‐ and regioselectivity, availability of starting materials and excellent yields (up to quantitative) of target products having rich functionality patterns for further derivatization.

A novel base-catalyzed synthesis of hitherto unknown 4-allyl-2-methylene-3(2H)-furanones from skipped diynones and allylic alcohols via nucleophilic addition/Claisen rearrangement/cyclization reaction is described. An important role of the employed catalytic system for the regioselective switching in the cyclization step from 3-allyl-4-pyrones to isomeric 4-allyl-3(2H)-furanones is discussed. The isolation of main intermediates of the tandem reaction and study of their reactivity allowed us to develop a convenient two-stage protocol for stereoselective 4-allyl-2-methylene-3(2H)-furanone formation featuring a good substrate tolerance and good yields of target products.

This comprehensive review summarizes the published literature data concerning the chemistry of α‐enolizable alkynones, also denoted aliphatic or C−H active alkynones, where an alkyl group is adjacent to the carbonyl function, from the first example in 1949 to the present day. Starting from a historical perspective, the reader will be introduced to the recent achievements and future challenges in this field. The review covers around 100 references.

A novel catalyst‐ and solvent‐controlled dimerization of aliphatic alkynones through tandem Michael addition/rearrangement/cyclization sequence has been developed. The elaborated protocol provides a convenient chemo‐, regio‐ and stereoselective access to rare 3(2H)‐furanones decorated with 2‐exo‐methylene and 4‐ethenyl functionalities. A comprehensive density functional theory (DFT) study of possible reaction mechanism including ab initio molecular dynamics (AIMD) simulations and quantum theory of atoms in molecules (QTAIM) analysis of various substrate/catalyst/solvent complexes has revealed the Janus‐like behavior of the employed sodium tert‐butoxide/toluene system that is responsible both for the chemoselectivity of the initial addition step and the inhibition of the final cyclization step.

The review summarizes the results and prospects of studying the reactions of acetylene with secondary alkyl ketoximes containing only one C–H bond at the α-position with respect to the oxime group in superbasic medium. The selective formation of key intermediate products in the pyrrole synthesis (3 H -pyrroles and 5-hydroxypyrrolines), their reactivity, and unique cascade assemblies of unexpected compounds are discussed.

The present work focuses on a comprehensive density functional theory (DFT) study of newly discovered base-catalyzed substrate-controlled dimerizations of aliphatic alkynones. In order to understand the origin of selectivity of the cascade assemblies of 6-methylene-5-oxaspiro[2.4]heptanones and 2-alkenylfurans, structural and electronic properties of neutral and deprotonated alkynone molecules, thermodynamic and kinetic characteristics of the deprotonation of alkynones having diverse C-H active substituents at the carbonyl function under the action of a base, and thermodynamic and kinetic characteristics of possible mechanisms of the discussed cascade reactions were theoretically assessed. The obtained computational results have confirmed and clarified an early qualitative assumption on the key role of the nature of the aliphatic substituent. Apart from fully rationalizing the experimental results, the theoretical DFT data give valuable details and data for predicting the outcome of related base-catalyzed reactions between various electrophilic substrates and nucleophilic species formed from C-H active aliphatic alkynones.

An expedient synthesis of hitherto unknown pyrrolo[2,1‐ a ]isoquinolinium salts from non‐aromatic aryl‐substituted 2 H ‐ and 3 H ‐pyrroles and internal alkynes has been developed. The process represents a rare example of N‐nucleophilic reaction of 2 H ‐ and 3 H ‐pyrroles and relies on the ortho ‐C−H bond activation of non‐aromatic arylpyrroles in the presence of rhodium catalyst followed by alkyne annulation reaction. A broad range of diversely substituted salts was obtained in high yields under mild reaction conditions. The photophysical properties for selected representatives of novel pyrrolo[2,1‐ a ]isoquinolinium salts have been evaluated to demonstrate their potential as fluorescent materials for light‐emitting devices and bioimaging.

A simple method to access tetrahydropyrrolo[1,2- d ]oxadiazoles in a diastereoselective manner starting from available pyrrolines and in situ generated nitrile oxides was developed.