Nguyen Trong Anh

Simple prediction of cycloaddition orientation: I—Diels-alder reactions

Abstract Application of the “hard and soft” concept to the Woodward-Katz model allows simple and accurate prediction of the structure of the major adduct in Diels-Alder reactions. About 100 examples have been examined. Agreement with experimental results is excellent: therefore, the doubts expressed by Houk et al.36 are groundless. Two special cases deserve mention. First, for compounds with heteroatoms at reactive sites, it is necessary to introduce explicity the overlap integrals in the perturbational treatment. Second, in the reactions between electron-poor dienes and nitrosobenzene derivatives the adjacent lone pairs on N and O play an important role.

Sur l'orientation syn-anti dans les reactions de Diels-Alder

Resume It is suggested that the syn-anti orientation in Diels-Alder reactions can be explained satisfactorily only if orbital factors and van der Waals-London interactions are both taken into account.

Factors controlling the regioselectivity of additions to α-enones—III: Reactions of 3-aryl α-enones with phosphorylated anions

Abstract Reaction of phosphonoester 2 and phosphononitrile 3 with chalcone and p -methoxychaleone in THF-t-BuOK at room temperature gives only the product resulting from CC double bond attack. The same reagents with benzalacetone lead to mixture of products resulting from CC double bond and carbonyl attack, though phosphine oxide 4 gives only the products of CC attack. Dypnone gives products of carbonyl attack with 3 and does not react with 2 . These results are discussed in terms of perturbation theory: C 4 attack increases with delocalization of the reagents negative charge and lowering of the α-enone LUMO level.

La regle d'alder generalisee: Role privilegie du substituant donneur d'electorns

Resume It is shown that, given a diene substituted with a donor D and a dienophile substituted with an attractor A. the reaction rate will generally decrease when the addends exchange their substituents, i.e. A going to the diene and D to the dienophile. Donor substituents are more effective in raising an HOMO than an attractor in lowering a LUMO of a conjugated substrate. It follows that for thermal symmetry-allowed cycloadditions between acyclic systems, the greatest rate increase is expected when the donor substituent is put on the compound with the higher HOMO (usually the more conjugated compound) and the attractor on the compound with the lower HOMO. This does not mean “put the donor on the donor and the attractor on the attractor”: butadiene is simultaneously a better donor and a better acceptor than ethylene. Some kinetic effects of bridging groups in cyclic systems are discussed.

Simple prediction of regiospecificity in Diels–Alder reactions

Application of the “hard and soft” concept to the Woodward–Katz model allows simple and accurate prediction of the structure of the major product in Diels–Alder reactions.

Simple prediction of cycloaddition orientation: II—2+2 thermal cycloadditions. Scope and limitations of the method

Abstract In the accompanying paper, it has been suggested that, in a cycloaddition, the first σ bond to be formed is that corresponding to the greatest overlap stabilization. This rule has now been tested, successfully on over one hundred 2+2 cycloadditions. Comparisons of our method with other theoretical treatments are made and the reasons for the discrepancies pointed out. The choice of parameters (for Huckel calculations) or molecular geometries (for CNDO/2 calculations) is discussed. No particular advantage of CNDO/2 calculations over Huckel calculations has been observed.

On the Use of Aromaticity Rules, Frontier Orbitals and Correlations Diagrams. Some Difficulties and Unsolved Problems

The most usual difficulties encountered in the study of frontier-controlled reactions by approximate methods (aromaticity rules, frontier-orbital approximation and correlation diagram) are reviewed.

Theoretical study of electrocyclic ring opening of oxirane.

Abstract SCF+CI calculations are performed to investigate the potential energy surface associated with the thermal C-C ring opening of oxirane (CH 2 OCH 2 ). Conrotatory, disrotatory and non-synchronous processes are studied, and the results discussed with respect to experimental data (Huisgen and toll.) which indicate a loss of stereoselectivity in the ring opening reactions of some substituted oxirane molecules.