Annulation Reactions of Allene-Derived 1,3-Dipole with 3-Substituted-Chromones:  Unusual Recognition of 4π-Component in 3-(N-Aryliminomethyl)chromones through [4 + 3] Annulation

Abstract

All-carbon dipole derived by the interaction of triphenylphosphine with allenic ester is able to locate the polarized 2pi-component in 3-formylchromones through a regioselective [2 + 3] addition to the C2-C3 pi-bond, which is followed by deformylation leading to novel 3a,9a-dihydro-1-ethoxycarbonyl-1-cyclopenteno[5, 4-b]benzopyran-4-ones. On the contrary, the dipole recognizes azadiene in 3-(N-aryliminomethyl)chromones through [4 + 3] annulation and initially formed adducts undergo tandem rearrangements to afford novel N-aryl-2, 3-dihydro-4-ethoxycarbonylchromano[2,3-b]azepine-6-ones in good yield.

Studies on the asymmetric, phosphine-promoted [3+2] annulations of allenic esters with 2-aryl-1,1-dicyanoalkenes

“…6 Other classes of electron-deficient olefins were shown to be competent substrates for [3+2] annulations with allenoates, however, asymmetric variants of these reactions have not been reported so far. Examples include annulations on a,b-unsaturated a-aminoacid derivatives 7 and amides, 8 tropone, 9 chromones, 10 and acrylonitrile. 11 In this context, the aim of enlarging the scope of enantioselective cyclizations on allenoates prompted us to investigate the use of chiral phosphines as catalysts for [3+2] annulations on a special class of electron-deficient a,b-unsaturated olefins, that is, arylidene malononitriles.…”

SOLVENT FREE SYNTHESIS OF PYRROLO[2,1-a]ISOQUINOLINES UNDER MICROWAVE-IRRADIATION: AN ANTIOXIDANT POTENT.

“…The intermediate B after subsequent deformylation [26] and pyrone ring cleavage [27] leads to intermediate C, which finally oxidizes to afford 3a. …”

Phosphine catalysis of allenes with electrophiles

“…37 In the mechanism proposed (Scheme 11), α-addition of the phosphonium dienolate 5 to the chromon 86 forms the intermediate 88 , which undergoes intramolecular cyclization and phosphine elimination to afford the [4+3] annulation product 90 . Thermal opening of the chromone ring in compound 90 generates the intermediate 91 ; subsequent rotation around a C–C single bond, recyclization of the chromone ring, and a 1,5-H shift in 93 affords the final product 87 .…”