Search results for "Electrocyclic reaction"
showing 4 items of 4 documents
Thermal 1,6-Electrocyclization Reactions of Acceptor-Substituted 2,3-Divinyl-1H-indoles Yielding Functionalized Carbazoles
1990
Three new synthetic procedures for and thermal 1,6-electrocyclizations of acceptor-substituted 2,3-divinyl-1H-indoles leading to functionalizing carbazoles are described. The scope and limitations as well as some mechanistic aspects of the methodologies are discussed. The key strategies employed include Pd(II)-catalyzed coupling and Wittig procedures.
Nature of the ring-closure process along the rearrangement of octa-1,3,5,7-tetraene to cycloocta-1,3,5-triene from the perspective of the electron lo…
2011
We analyze the behavior of the energy profile of the ring-closure process for the transformation of (3Z,5Z)-octa-1,3,5,7-tetraene 5 to (1Z,3Z,5Z)-cycloocta-1,3,5-triene 6 through a combination of electron localization function (ELF) and catastrophe theory (CT). From this analysis, concepts such as bond breaking/forming processes, formation/annihilation of lone pairs, and other electron pair rearrangements arise naturally through the reaction progress simply in terms of the different ways of pairing up the electrons. A relationship between the topology and the nature of the bond breaking/forming processes along this rearrangement is reported. The different domains of structural stability of …
The electronic substituent influence on the thermally allowed electrocyclic interconversion cyclobutene/butadiene. A MNDO study
1984
The effects of donor/acceptor substitution on the conrotatory cyclobutene/butadiene interconversion have not yet been experimentally studied. MNDO Synchronous Transit/MINIMAX calculations for all possible combinations of NH2/NH3 + 3 groups at the fissile single bond reveal very large substituent effects on the opening reactions and reverse cyclisations. Diamino(1b/2b), diammonio-(1c/2c) and amino-ammonio-substitutions (1d/2d) change the activation energy of the reference ring opening reaction (1a →2a) from 49.9 kcal/mol to 34.7, 29.8 and 26.0 kcal/mol, respectively. This rate enhancement parallels the monotone shift of the transition state pathcoordinate towards the cyclobutenes. Relative t…
Cyclocondensation of alpha-aminonitriles and enones: a short access to 3,4-dihydro-2H-pyrrole 2-carbonitriles and 2,3,5-trisubstituted pyrroles.
2009
The reaction of alpha,beta-unsaturated carbonyl compounds with aminoacetonitrile hydrochloride furnishes 3,5-disubstituted 3,4-dihydro-2H-pyrrole-2-carbonitriles in a one-pot reaction sequence. While these products can serve as starting materials for the preparation of polysubstituted pyrrolizidines, they are kinetically stable against the base-induced elimination of HCN. In contrast, their 2-substituted analogues obtained from alpha-substituted alpha-aminonitriles can be readily converted to the corresponding 2,3,5-trisubstituted pyrroles under microwave irradiation. The key step presumably involves the thermal electrocyclization of a stabilized 2-azapentadienyl anion formed by condensatio…