Ab initio and DFT quantum chemical calculations have been applied to a study of the Diels-Alder reaction of o-benzoquinone as diene and norbornadiene as dienophile. Transition states for the different reactions are located and activation energies estimated. The prefered exo-π-facial selectivity and exo,endo-stereoselectivity exhibited in this cycloaddition are readily predicted using RHF/3-21G ...

The combination of two or more unsaturated structural units to form cyclic organic compounds is commonly referred to as cycloaddition, and the combination of two unsaturated structural units that forms a six-membered ring is formally either a [5 + 1]-, [4 + 2]-, [2 + 2 + 2]-, or [3 + 3]-cycloaddition. Occurring as concerted or stepwise processes, cycloaddition reactions are among the most usefu...

The enzyme SpnF, involved in the biosynthesis of spinosyn A, catalyzes a formal [4+2] cycloaddition of a 22-membered macrolactone, which may proceed as a concerted [4+2] Diels-Alder reaction or a stepwise [6+4] cycloaddition followed by a Cope rearrangement. Quantum mechanics/molecular mechanics (QM/MM) calculations combined with free energy simulations show that the Diels-Alder pathway is favo...

New routes to the synthesis of various novel chiral maleimides are described. The oxabicyclic anhydride 2 readily available exo-Diels-Alder adduct of furan and maleic anhydride was used as a vehicle, which in turn reacted with hydrochlorides of amino acids 3a-f in the presence of Et3N with release of furan to give the requisite novel chiral imides 4a-f in good to moderate yields. The stereosele...

We examined the catalytic activity of substituted thioureas in a series of Diels-Alder reactions and 1,3-dipolar cycloadditions. The kinetic data reveal that the observed accelerations in the relative rates are more dependent on the thiourea substituents than on the reactants or solvent. Although the catalytic effectiveness is the strongest in noncoordinating, nonpolar solvents, such as cyclohe...

N-heterocyclic carbene (NHC) catalysis has emerged as a powerful tool for synthesis. Among its involvement in several cycloaddition-type reactions for the construction of lactams and lactones, which are abundant in biologically active molecules and broadly used as synthons for complex molecules, NHC catalysis through formal [3+3] or [4+2] strategies is noteworthy. In particular, [4+2] cycloaddi...

A solid-phase strategy using lipase as a biomolecular scaffold to produce a large amount of Cu(2+)-metalloenzyme is proposed here. The application of this protocol on different 3D cavities of the enzyme allows creating a heterogeneous artificial metallolipase showing chimeric catalytic activity. The artificial catalyst was assessed in Diels-Alder cycloaddition reactions and cascade reactions sh...

The first enantioselective total syntheses of prenylflavonoid Diels-Alder natural products (-)-kuwanon I, (+)-kuwanon J, (-)-brosimone A, and (-)-brosimone B have been accomplished from a common intermediate based on a concise synthetic strategy. Key elements of the synthesis include a biosynthesis-inspired asymmetric Diels-Alder cycloaddition mediated by a chiral ligand/boron Lewis acid, as we...

During the last two decades, organic reactions in aqueous media have been attracting increasing attention. Furthermore, It has been established that some DielsAlder reaction dramatically accelerated in aqueous media. These have been alternatively ascribed to hydrophobic association of the reacting partners, micellar catalysis, solvophobicity, high internal solvent pressure, cohesive energy dens...