The pericyclic reactions of 2,5-bis(methoxycarbonyl)-3,4-diphenylcyclopentadienone (1a) with both allylic and propargylic amines have been investigated. The reaction proceeded via initial formation of the 1,4 adducts followed by the ene cyclization and/or sequential pericyclic reactions depending upon the structures of the amines. The reaction of 1a with diallylamine (2a) gave the tetracyclic compound (3a). On the other hand, the reaction of 1a with 2-propynylamine (2c) gave exclusively the bicyclic compound (5c). In the reactions with the secondary 2-propynylamines (2d,e), the tetracyclic compounds (3d,e) were exclusively formed. The reactions of 1a with alpha-branched primary 1,1-dialkyl-2-propynylamines (2f,g) gave mixtures of 3- and 5-type compounds. The tetracyclic compounds 3 were formed from the intramolecular [4+2]pi cycloadditions of the [1,5]-sigmatropic rearrangement products of the 1,4 adducts of 1a and 2, followed by the [1,5]-sigmatropic rearrangement of hydrogen and dehydrogenation. The bicyclic compounds 5 were derived from the [2pi+2pi+2sigma] reaction of the 1,4 adducts of 1a and 2. The one-pot multistage sequential pericyclic reactions were discussed on the basis of the X-ray crystallographic structures and the MO calculation data.

Treatment of 2,5‐bis(methoxycarbonyl)‐3,4‐diphenylcyclopentadienone (1) with aniline (2a) gave the stereoisomeric 2‐anilino‐2,5‐bis(methoxycarbonyl)‐3,4‐diphenylcyclopentenones (cis‐ and trans‐4a). 1H NMR spectroscopic monitoring of the reaction indicates that both compounds are derived from the 1,5‐sigmatropic rearrangement of the 1,4‐addition products cis‐ and trans‐3a. The structure of 3a was established by the X‐ray analysis of the product after methylation (3a‐Enol‐Me) with diazomethane. The sequential pericyclic reaction behavior of 1 with amines is discussed on the basis of X‐ray crystal structures and the optimized structure of the transition state at the B3LYP/6−31G(d) level of theory. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

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