DFT study on the cycloaddition reactions of [c]-annelated carbo- and heterocyclic five-membered dienes with ethyleneElectronic supplementary information (ESI) available: figures and tables of the principal geometric parameters of all the dienes, transition states and products obtained at the B3LYP/6-31G* level and the Cartesian coordinates of all the optimized structures considered in this study. See http://www.rsc.org/suppdata/p2/b2/b205663a/

Abstract

B3LYP/6-31G* calculations were done on a series of [c]-annelated heterocyclic five-membered dienes and their cycloaddition transition state structures and products. Cyclobutano[c]-, cyclobuteno[c]-and benzo[c]-fused fivemembered rings represent non-aromatic, antiaromatic and aromatic ring fused dienes, respectively, and their reactivity was studied with ethylene as dienophile. In the cases of cyclobutano-and cyclobuteno-fused dienes, the fused portion remains a mere spectator and no significant geometric variations are seen along the reaction coordinate. In contrast, in the benzo-fused systems, the fused benzene ring witnesses significant changes in the bond lengths along the reaction coordinate highlighting the active participation of the π-framework in the reaction. Thus, this may be classified as an [8 ϩ 2] cycloaddition. The benzo[c]-fused rings exhibit the lowest activation energies followed by cyclobutano and cyclobuteno analogues, and the exothermicities decrease in the same order. A linear relationship between the reaction exothermicity and activation energy is obtained for the systems under consideration. The percentage bond length alternation on going from reactant to transition state, the Fukui function indices and frontier orbital analysis, extent of charge transfer from diene to dienophile at the transition state, and deformation energies were estimated to explain the reactivity of the dienes with ethylene.

Theoretical studies of a singlet oxygen-releasing dioxapaddlane (1,4-diicosa naphthalene-1,4-endoperoxide)

“…Masked dienes such as compound 19 are similar to the naphthalene compounds studied here, in which DFT methods often yield results in excellent agreement with experiment [68-74]; although, the B3LYP functional is not devoid of shortcomings especially with larger sized molecules [75, 76]. We find the decomposition of endoperoxides 2, 6, 14, 16 , and 18 to be endothermic by 6–17 kcal/mol (Table 1).…”

“…The decomposition of naphthalene endoperoxides is reminiscent of retro Diels–Alder reactions of “masked” dienes (Scheme 5) [68-71]. Masked dienes such as compound 19 are similar to the naphthalene compounds studied here, in which DFT methods often yield results in excellent agreement with experiment [68-74]; although, the B3LYP functional is not devoid of shortcomings especially with larger sized molecules [75, 76].…”

Comparative Study on the Structural, Optical, and Electrochemical Properties of Bithiophene‐Fused Benzo[c]phospholes

“…As shown in The structures of these compounds were optimized at the B3 LYP/6-31G* level, which is the same as that used for the theoretical calculation of unsubstituted benzo[c]phosphole. [11,25] The bond lengths and bond angles at the p-conjugated units of 4 m, 5 m, and 10 m are close to the respective values of 4 a, 5 a, and 10 a determined by X-ray crystallography ( Figure S4 in the Supporting Information). As visualized in Figure 5 As seen in Figure 5, the HOMO and LUMO energies of the P-oxo models 10 m-12 m are lower by 0.40-0.42 eV and 0.78-0.81 eV, respectively, than those of the s 3 -P models 4 m-6 m. Hence, the HOMO-LUMO gaps of 10 m-12 m become narrower by 0.36-0.41 eV relative to those of 4 m-6 m. Evidently, the oxygenation at the phosphorus center stabilizes the LUMO more than the HOMO, due to the effective s*-p* orbital interaction.…”

“…[11] Taking the calculated HOMO and LUMO energies into consideration, the authors predicted that benzo[c]phosphole would be an attractive platform for the construction of novel phosphole-based pconjugated systems with a low-lying LUMO and a relatively small HOMO-LUMO gap. Noticeably, the LUMO energy and the HOMO-LUMO gap of benzo [c]phosphole (E LUMO = À1.97 eV and DE H-L = 3.29 eV calculated at the B3 LYP/6-31G* level) are much lower and narrower, respectively, than those of dibenzoA C H T U N G T R E N N U N G [b,d]phospholes (E LUMO = À0.98 to À0.97 eV and DE H-L = 4.94-4.95 eV calculated at the same level), [12] implying that the position of fused ring(s) dramatically affects the nature of frontier orbitals.…”

Competitive Diels−Alder Reactions: Cyclopentadiene and Phospholes with Butadiene

“…Cycloaddition reactions are versatile synthetic organic routes in obtaining complex molecular architectures and particularly, [4+2] Diels−Alder cycloaddition reactions have been indispensable tools for successful syntheses of novel molecular targets. − Cycloaddition reactions of phospholes have been employed to access novel polycyclic organophosphorus compounds. Many of the phosphorus-containing cycloadducts have promising applications in the fields of homogeneous catalysis and molecular materials. − [4+2] cycloaddition reactions of phospholes with various dienophiles have been the subject of both experimental 6-15 and theoretical interest. − The notable contribution of Mathey's group has received special attention in the chemistry of phospholes that includes the cycloaddition with a wide range of dienophiles, interconversion of phospholes through a [1,5] sigmatropic shift, cyclodimerizations, enhancing the reactivity of phospholes by different substituents, reactions with transition metal derivatives to give organometallic complexes and applications of compounds derived from phospholes. − …”