Pentadienyl Cation Research Articles

Theoretical Studies of the Nazarov Cyclization 1. 1,4-Pentadien-3-one.

The mechanism of the electrocyclization of 1,4-pentadien-3-one, known as the Nazarov cyclization, was studied using semiempirical and ab initio methods at the AM1, RHF/3-21G, RHF/6-31G and MP3/6–31G **//RHF/3-21G or RHF/6–31G * levels. At the highest level of theory, the cyclization of the protonated ketone, 2, to the protonated cyclopentenyl system 3 is exothermic by 2.3 kcal/mol with an activation energy for this reaction of 20.6 kcal/mol. The transition state occurs late along the reaction coordinate, with the newly forming carbon-carbon bond length 2.09 angstroms. These values are in sharp contrast to those calculated for electrocyclization of the pentadienyl cation.

Theoretical predictions of torquoselectivity in pentadienyl cation electrocyclizations

Theoretical predictions of torquoselectivity in pentadienyl cation electrocyclizations

Bitter Principles of Ailanthus altissima Swingle. Conversion of Ailanthone into Shinjulactone C

Abstract Ailanthone was converted into shinjulactone C with a hexacyclic 1α,12α:5α,13α-dicyclo-9βH-picrasane skeleton. The key reaction consists of an intramolecular ionic [4+2] cycloaddition between a pentadienyl cation and an olefin.

Conversion of ailanthone into shinjulactone C through an ionic [4+2] cycloaddition reaction

Ailanthone was converted into shinjulactone C with a 1α,12α: 5α,13α-dicyclo-9β H-picrasane skeleton. The key reaction consists of an intra-molecular ionic [4+2] cycloaddition between a pentadienyl cation and an olefin.

ChemInform Abstract: ACID‐CATALYZED OLIGOMERIZATION BETWEEN 4‐(1‐ETHYL‐1‐PROPENYL)MORPHOLINE AND BENZYLIDENEANILINES. SYNTHESIS OF 1,2,3,4,7A,8‐HEXAHYDRO‐4‐AZA‐S‐INDACENE DERIVATIVES

AbstractDie Benzyliden‐aniline (II) reagieren mit dem Enamin (I) in Essigsäure zu Cyclisierungsprodukten (III).

ACID-CATALYZED OLIGOMERIZATION BETWEEN 4-(1-ETHYL-1-PROPENYL)MORPHOLINE AND BENZYLIDENEANILINES. SYNTHESIS OF 1,2,3,4,7a,8-HEXAHYDRO-4-AZA-s-INDACENE DERIVATIVES

Abstract Reaction of 4-(1-ethyl-1-propenyl)morpholine with benzylideneanilines in acetic acid provided 1,2,4,6,7-pentaaryl-3,5,7a-trimethyl-1,2,3,4,7a,8-hexahydro-4-aza-s-indacene in decent yield. The reaction mechanism involving the conrotatory cyclization of an intermediate pentadienyl cation has been proposed.

Electrocyclic reactions. Part III. Some reactions of 2,4-dimethyl-1,5-diphenylpenta-1,4-dien-3-one (αα′-dimethyldibenzylideneacetone)

αα′-Dimethyldibenzylideneacetone (I) by treatment with hot hydrochloric acid givestrans-2,5-dimethyl-3,4-diphenylcyclopent-2-enone (Va). With hot hydriodic acid the minor product is the cyclopentenone (Va) and the major product is trans-2,5-dimethyl-trans-3,4-diphenylcyclopentanone (VIa). The cyclopentenone (Va) undergoes only partial reduction with hot hydriodic acid to the cyclopentanone (VIa). The results suggest a conrotatory thermal ground state electrocyclisation of a pentadienyl cation to a cyclopentenyl cation, followed by loss of a proton and ketonisation, or by reduction. The high yields of cyclic products, relative to those observed for trans,trans-dibenzylideneacetone, are notable.

Electronic Structures of the Ring-Protonated Aromatic Amines

Abstract In order to study the electronic spectra and stabilities of the ring protonated aromatic amines, π-electron structure of nineteen amino-substituted pentadienyl cations were calculated by the composite molecule method. The lower electronic transitions of these ions are assigned to the charge transfer from amino groups to the pentadienyl cation. Stability of the ground state depends on the extent of intramolecular charge transfer, which is determined by the position and number of amino-substitution. The amino group on 1-, 3- or 5-carbon atom greatly stabilizes the ground state while contribution of the amino group on the other position is quite small. Occurrence of the ring or amino protonation for various amino-substituted benzenes is shown to be well predicted by the calculated stabilization energy.

Valence bond treatment of systems involving orbital degeneracy

Ground and excited electronic states of the allyl cation and anion, the butadiene radical cation and anion, and of the pentadienyl cation and anion have been calculated by a semiempirical valence bond method. The results of such calculations are in essential agreement with the known properties of such systems. A comparison of the results of the valence bond treatment with those expected on the basis of the qualitative resonance theory yields serious discrepancies which show up the limitations inherent in the latter formalism.