Showing papers by "James P. Snyder published in 1997"
92 citations
TL;DR: A detailed computational study was undertaken to provide better insight into the factors that influence the intramolecular cycloaddition process and indicates that a severe cross-ring 1,3-diaxial interaction caused by the bridgehead methyl group promotes a boat or twist-boat conformation in the piperidine ring fused to the newly forming one.
Abstract: A series of diazoamido keto esters were prepared by the reaction of N-substituted 3-carbethoxy-2-piperidone with n-butylmagnesium chloride followed by the addition of ethyl 2-diazomalonyl chloride. Treatment of these diazo amides with rhodium(II) acetate afforded transient push−pull carbonyl ylide dipoles which could be readily trapped with electron deficient dipolarophiles. All attempts to induce the dipolar cycloaddition to occur across tethered alkenyl π-bonds failed to give internal cycloadducts. However, placing a sp2 center on the tethered side chain was found to result in the formation of a tricyclic adduct in 95% yield. The stereochemistry of the cycloadduct was firmly established by an X-ray crystallographic study and occurred endo with respect to the amido carbonyl ylide dipole. A detailed computational study was undertaken to provide better insight into the factors that influence the intramolecular cycloaddition process. The calculations indicate that a severe cross-ring 1,3-diaxial interaction...
47 citations
TL;DR: To examine the amine vs amide influence on the course of intramolecular cycloaddition, density functional theory (DFT) calculations have been carried out and results strongly suggest that the amide-substituted isobenzofurans are destabilized by steric effects between the aromatic ring and the nitrogen-containing side chain.
Abstract: The α-thiocarbocation generated from the Pummerer reaction of an o-amido-substituted sulfoxide is intercepted by the adjacent amido carbonyl group to produce a 2-amino-substituted isobenzofuran as a transient intermediate. In the presence of an electron-deficient dienophile, the reactive isobenzofuran undergoes a Diels−Alder cycloaddition followed by ring opening to furnish a vinylogous C-acyliminium ion that readily aromatizes. The one-pot intramolecular cascade process only occurs either if the olefinic tether is activated by an ester or if a carbonyl group is located adjacent to the nitrogen atom of the 2-amino-substituted isobenzofuran. To examine the amine vs amide influence on the course of intramolecular cycloaddition, density functional theory (DFT) calculations have been carried out for both ground and transition states. The results strongly suggest that the amide-substituted isobenzofurans are destabilized by steric effects between the aromatic ring and the nitrogen-containing side chain. Raisin...
30 citations
TL;DR: In this article, the synthesis of regioisomeric bicyclo derivatives is described, with an approach that entails as a key step the formation of a twelve-membered ring by an unprecedented intramolecular Dieckmann cyclisation.
6 citations