Search

The design of various cycloaddition/annulation processes is one of the most intriguing challenges in the development of donor-acceptor (D-A) cyclopropane chemistry. In this work, a new class of formal high-order [6+n]-cycloaddition and annulation processes of D-A cyclopropanes with cycloheptatriene systems has been designed and reported, to fill a significant gap in the chemistry of D-A cyclopropanes. The reactivity of methylated cycloheptatrienes from Me1 to Me5 as well as unsubstituted cycloheptatriene was studied in detail under GaCl 3 activation conditions, which makes it possible to efficiently generate gallium 1,2-zwitterionic complexes or 1,3-zwitterionic intermediates starting from D-A cyclopropanes, while other Lewis acids are ineffective and non-selective. New examples of formal [6+2]-, [6+3]-, [6+4]-, [6+1]-, and [4+2]-cycloaddition and annulation reactions with cycloheptatrienes along with more complex processes were discovered. Cycloheptatriene itself can also successfully act as a hydride anion donor, which allows the ionic hydrogenation of D-A cyclopropanes to be performed under mild conditions. As a result, a number of efficient and highly diastereoselective protocols for the synthesis of seven-membered carbocycles has been developed., (© 2024 Wiley-VCH GmbH.)

Antiaromatic nucleophilic substitution reactions in cycloheptatrienide pyridinium and phosphonium zwitterions with initial formation of a cycloheptatetraene intermediate are explored. The mechanism was supported by quantum chemical calculations, first-order reaction kinetics, and high-resolution mass spectrometry. The pyridinium zwitterion exhibited weak antiaromaticity, whereas the intermediate displayed Möbius aromaticity, as evidenced by nuclear independent chemical shift values and the shape of its HOMO. This study represents the eighth confirmed instance of a Möbius-aromatic organic species in its ground state.

Investigations of the nature and degree of antiaromaticity of cycloheptatrienyl anion derivatives using both experimental and computational tools are presented. The ground state of cycloheptatrienyl anion in the gas phase is triplet, planar and Baird-aromatic. In DMSO, it assumes a singlet distorted allylic form with a paratropic ring current. The other derivatives in both phases assume either allylic or diallylic conformations depending on the substituent pattern. A combination of experimental and computational methods was used to determine the pK a values of 16 derivatives in DMSO, which ranged from 36 to -10.7. We revealed that the stronger stabilization of the anionic system, which correlates with acidity, does not necessarily imply a lower degree of antiaromaticity in terms of magnetic properties. Conversely, the substitution pattern first affects the geometry of the ring through the bulkiness of the substituents and their better conjugation with a more distorted system. Consequently, the distortion reduces the cyclic conjugation in the π-system and thereby decreases the paratropic current in a magnetic field, which manifests itself as a decrease in the NICS. The triplet-state geometries and magnetic properties are nearly independent on the substitution pattern, which is typical for simple aromatic systems., (© 2024 Wiley-VCH GmbH.)

An approach to the synthesis of seven-membered systems via the chain elongation of nucleophilic propenes and subsequent 8π-electrocyclization is proposed. The cascade reaction yields either cycloheptadienes or bicycloheptenes, and the latter are formed via a 6π-electrocyclization of intermediate cycloheptadienyl anion which was proved to be reversible in a basic medium. The electrocyclic nature of the ring-closing reactions was supported by density functional theory and DLPNO/CCSD(T) calculations. Highly electron-deficient cycloheptatrienes can be obtained from cycloheptadienes or bicycloheptenes via oxidation either introduced into the cascade reaction or performed as a separate reaction, with the overall yield of up to 81%. The oxidation step was performed by means of a rarely encountered Cu(II)-catalyzed dehydrogenation of cycloheptadienes or bicycloheptenes, and so the reaction mechanism was proposed. Stable formally 8π-antiaromatic cycloheptatrienyl-anion containing compounds were obtained, and some correlations between their UV-vis spectra and the structure of the distorted cycloheptatrienyl-anion moiety were clarified. Additionally, a base-induced retro-[2 + 2]-cycloaddition in a bicycloheptene derivative gave cyanotetra(methoxycarbonyl)cyclopentadienyl cesium.

During intracranial surgical interventions, the major tasks of an anesthetic procedure are to maintain cerebral perfusion, adequate oxygen delivery, and brain tissue metabolism at all surgical stages. The authors have compared cerebral metabolism and the exchange of biogenic amines that regulate cerebral oxygen consumption and cerebral blood flow, by using neuroleptic anesthesia and balanced anesthesia on the basis of enflurane during operations on intracranial vessels. There is evidence for the equal efficiency of both types of anesthesias and for a unidirectional impact on the body's neurohumoral systems.