466686-19-1Relevant articles and documents
Electrocyclization reactions of 1-Aza- and 1-oxapentadienyl and -heptatrienyl cations: Synthesis of pyrrole and furan derivatives
Alickmann, Dirk,Froehlich, Roland,Maulitz, Andreas H.,Wuerthwein, Ernst-Ulrich
, p. 1523 - 1537 (2007/10/03)
Quantum chemical DFT calculations (B3LYP/6-31+G) have been used to gain insight into the conformational and energy properties of the 1-aza- and 1-oxapentadienyl and -heptatrienyl cations 1, 2, 3, and 4. The calculated thermodynamic and kinetic data of the ring-closure reactions giving the cyclic products 5-14 are reported and discussed with respect to the experimental results. Experimentally, synthetic routes to the α,β-unsaturated carbonyl compounds 24 and 27, each with a leaving group in the γ-position, have been developed. These compounds have been investigated with respect to their ability to undergo 1,5-electrocyclization reactions to yield 2,5-disubstituted furans 28 upon heating in the presence of acid, presumably through the intermediate formation of the 1-oxapentadienyl cations 2. From the corresponding imine 29a the pyrrole 30d was obtained after treatment with tetrakis (triphenylphosphane) palladium. In the presence of benzylamine and the Pd° catalyst, the corresponding pyrroles 30a-c were formed from 24 and 27. The homologous α,β,γ,δ-unsaturated carbonyl compounds 31 afforded 2-vinyl-substituted furans 32 upon heating with acid, and the 2-vinyl-substituted pyrroles 34 on treatment with benzylamine and the Pd catalyst. No seven-membered heterocyclic rings were formed. Surprisingly, the α,β-unsaturated carbonyl compounds with two phenyl substituents at the γ-position also provided pyrrole derivatives 40 through a formal dimerization. Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002.
