Arylmethylene derivatives of 5-R-3H-furan-2-ones and N-aryl-5-R-3H-pyrrol-2-ones in reaction with acetylacetone

Abstract

The investigated compounds contain a conjugated oxoene fragment involving the exocyclic C=C bond and the double bond of the carbonyl group. Earlier [1] it was shown that the C=C and C=O bonds are fixed in the S-cis configuration, making it possible to use 3-arylmethylene-substituted furan-2-ones and pyrrol-2-ones in condensation reactions.The wide-ranging possibilities of using 3-arylmethylene-3H-furan-2-ones and N-aryl-3-arylmethylene-3H-pyrrol-2-ones in synthesis arise primarily from the presence of the two electrophilic centers. As a result of the delocalization of electron density in the C=C-C=O system these compounds behave as ambident electrophiles, and the addition of nucleophilic particles can take place in two directions, i.e., with attack at the carbon atom of the carbonyl group (1,2-addition) or at the β-carbon atom (1,4-addition).The relative reactivity of the 3-arylmethylene-3H-furan-2-ones and N-aryl-3-arylmethylene-3H-pyrrol-2-ones in 1,2-and 1,4-addition was examined by means of perturbation molecular orbital theory (PMO). According to this theory, if the electronic structure of the enone fragment is taken into account addition at the C=C group takes place under charge control while 1,4-addition (at the β-carbon atom) takes place under orbital control due to the maximum positive charge at the carbonyl carbon and maximum localization of the LUMO at the β-carbon atom.Orbital-controlled 1,4-addition is promoted by the increase in the degree of charge delocalization at the electrophilic center of the exocyclic C=C bond in the arylmethylene-substituted furanones, which is accompanied by a decrease in the LUMO energy level. For the initial arylmethylene-substituted 3H-furan-2-ones and N-aryl-3H-pyrrol-2-ones the electron densities of the LUMO at the exocyclic sp 2 -hybridized carbon atom were calculated by the LCAO-MO SCF method with PM3 parametrization in the MNDO approximation (Table 1). The results show that the electron density of the LUMO for the carbon atom of the exocyclic C=C bond is higher than that for the carbon atom of the carbonyl group, and on this basis it was concluded that 1,4-addition occurs in the case of the reaction with C-nucleophiles. __________________________________________________________________________________________

Structure, Z′ = 2 Crystal Packing Features of 3-(2-Chlorobenzylidene)-5-(p-tolyl)furan-2(3H)-one

“…Arylmethylidene derivatives are also available as scaffolds for the synthesis of various heterocyclic compounds of different complexity. These substances combine the properties of unsaturated carbonyl compounds and esters, allowing the implementation of reactions with various C-nucleophiles such as acetoacetic ester [ 18 ], acetylacetone [ 19 ], cyclohexanone [ 20 ], and mono- and N , N -binucleophiles [ 21 , 22 ]. Owing to the presence of a conjugated double bond, arylidene derivatives can easily add azides [ 23 , 24 ] oxygen (to give rise corresponding epoxides [ 25 ]), and halogen [ 26 ].…”