A possible mechanistic pathway related to an enzyme-catalyzed [4+2] cycloaddition reaction was studied by theoretical calculations at density functional (B3LYP, O3LYP, M062X) and semiempirical levels (PM6-DH2, PM6) performed on a model system. The calculations were carried out for the key [4+2] cycloaddition step considering enzyme-catalyzed biosynthesis of Spinosyn A in a model reaction, where...

This review presents the synergistic effect in the catalytic system of ionic liquids (ILs) for the synthesis of cyclic carbonate from carbon dioxide and epoxide. The emphasis of this review is on three aspects: the catalytic system of metal-based ionic liquids, the catalytic system of hydrogen bond-promoted ionic liquids and supported ionic liquids. Metal and ionic liquids show a synergistic ef...

Competitive retro-cycloaddition in [60]- and [70]fullerene homodimers (1a,1c) as well as [60]/[70]heterodimer (1b), linked through 2-pyrazolinopyrrolidino bridges, has been studied by means of HPLC, mass spectrometry, and theoretical calculations at the density functional theory (DFT) level by using the two-layered ONIOM approach. The results of these investigations indicate that the retro-cycl...

A series of 6-alkenyl-3-phenylcyclohex-2-enones has been synthesised and the structures of the products obtained from them on irradiation have been determined. The 6-propenyl compounds afforded a tricyclic 'parallel' [2 + 2] cycloaddition product and a bicyclic enone resulting from hydrogen abstraction in the biradical intermediate. The 6-butenyl and 6-pentenyl analogues gave 'crossed' cycloadd...

Abstract Terminal propargylic compounds containing an alkyne unit and an alcohol or ester group in the propargylic position have a fairly acidic acetylenic hydrogen atom; this makes them versatile substrates for further chemical transformation. Some transition metals such as ruthenium or copper exhibit specific affinity for terminal propargylic compounds, generating dielectrophilic ruthenium– o...

an efficient one-pot three-component procedure for the synthesis of new chiral spiro-oxindolopyrrolizidines with highly regio-, diastereo-, and enantioselective from 1,3-dipolar cycloaddition of azomethine ylides and optically pure active cinamoyl oxazolidinone are described. the process occurs at room temperature in aqueous ethanol as green solvent and in the absence of any bidentate chelating...

DFT calculations probing potential (4 + 2) and (4 + 3) cycloaddition pathways leading to the polycyclic ring systems found in the coral secondary metabolites plumarellide, mandapamate and rameswaralide are described. Formation of plumarellide and mandapamate via stepwise intramolecular cycloaddition of a furanoxonium ion onto a 1,3-diene is shown to be viable. The calculations also predict the ...

Several regioselectively π-extended, pyrrole fused porphyrinoids have been synthesized by the 1,3-dipolar cycloaddition of meso-alkylidene-(benzi)porphyrins. Pd(II) complexes gave oxidation resistant, bis-pyrrole fused adducts. The repeated 1,3-dipolar cycloaddition followed by oxidation-reduction of pentaphyrin analogs afforded π-extended porphyrin analogs.

We systematically examined the effect of different esters on the rhodium-catalyzed intermolecular [5+2] cycloaddition of 3-acyloxy-1,4-enynes and alkynes with a concomitant 1,2-acyloxy migration. Significant rate acceleration was observed for benzoate substrates bearing an electron-donating substituent. The cycloaddition can now be conducted under much more practical conditions for most termina...

Herein, we describe the first catalytic asymmetric intramolecular [4+2] cycloaddition of in situ generated ortho-quinone methides. In the presence of a confined chiral imidodiphosphoric acid catalyst, various salicylaldehydes react with dienyl alcohols to give transient ortho-quinone methide intermediates, which undergo an intramolecular [4+2] cycloaddition to provide highly functionalized fura...