Cyclobutadiene (CBD) displays aromaticity in the lowest-lying triplet excited state (T1) according to Baird's 4n electron rule. Hence, antiaromatic CBD in the T1 state has never been reported so far. Here we demonstrate via density functional theory (DFT) calculations that the CBD ring could possess dual antiaromaticity in the lowest singlet state (S0) and T1 states (termed as adaptive antiaromaticity), which is supported by various aromaticity indices including NICS, ACID, ΔBL, ELF and ISE.
Org. Chem. Front.
Organic Chemistry Frontiers
Asymmetric C(sp3)–H functionalization has emerged as a useful tool for simultaneous installation of functionality and chirality onto hydrocarbon units. Stereodiscrimination in reactions between a strong C(sp3)–H bond and a prochiral substrate, potentially forging vicinal stereogenic centers in a single step, however, remains a significant challenge. We report here a photocatalytic diastereo- and enantioselective C(sp3)–H functionalization/intramolecular cyclization reaction.
As an electron-rich species, radical anions have a wide range of applications in organic synthesis. In addition, aromaticity is an essential concept in chemistry that has attracted considerable attention from experimentalists and theoreticians. However, it remains unknown whether there is a relationship between aromaticity and thermodynamic stability of a radical anion. In this work, we demonstrate that the thermodynamically stable radical anions could be formed by the corresponding antiaromatic neutral species through density functional theory calculations.
The cyclobutane unit is important to prepare complex natural products with biological activity due to the high ring strain. Among various approaches, [2 + 2] cycloaddition is one of the major strategies to prepare cyclobutane under light conditions. Recently, Rajanbabu's group reported tandem catalysis for asymmetric coupling of inactivated ethylene and enynes to functionalized cyclobutenes or cyclobutanes. However, the reaction mechanisms remain unproven.
Olefin metathesis is a fundamental organic reaction of great importance that led to the 2005 Nobel Prize in Chemistry. As a variation of olefin–olefin metathesis, carbonyl–olefin metathesis (COM) is less developed, but still significant progress has been made recently. However, how the aromaticity affects the reaction mechanisms remains unclear. Here we perform density functional theory calculations on iron(III) catalyzed COM in 2,5- and 3,5-hexadienals.
Using density functional theory (DFT) calculations, the present study explores the mechanisms of two ruthenium(II)-catalyzed phosphoryl-directed ortho-selective C–H bond activation reactions. Depending on the nature of the phosphoryl groups, namely R2P(O) versus RP(O)OH, two different products could be selectively synthesized. For R2P(O), the overall catalytic cycle includes three basic steps: C–H bond activation, alkyne insertion, and protonation. The oxidation state of the Ru center does not change during this catalytic process.
Density functional theory (DFT) calculations were carried out to investigate the hydridic character of several main group hydrides. A P-hydrido-1,3,2-diazaphospholene 1f with two π-electron donor amino groups on the heterocyclic skeleton framework performs as a strong hydride donor owing to the significant n(N)–σ*(P–H) hyperconjugation. The natural bond orbital analysis reveals that high π-electron delocalization exists in both 1f and the corresponding stable phosphenium Ef+.