Ab initio and density functional calculations on the pericyclic vs pseudopericyclic mode of conjugated nitrile ylide 1, 5-electrocyclizations.

Ab initio (MP2/6-311+G and MP4(SDTQ)/6-311+G//MP2/6-311+G) and density functional (B3LYP/6-311+G) calculations on the ring closure reactions of conjugated nitrile ylides 1a-e, 3, and 6 to the corresponding oxazoles 2a, 5, 7, and 8; thiazoles 2b and 4; imidazole 2c; and pyrroles 2d and 2e, respectively, are reported. Vinyl nitrile ylides 1d and 1e cyclize with a substantially higher barrier than nitrile ylides containing a heteroatom. Geometric features as well as electronic structures as obtained by NBO analysis are indicative of a pericyclic, monorotatory 1, 5-electrocyclization of 1d and 1e.

Highly versatile solid phase synthesis of biofunctional 4-aryl-3,4-dihydropyrimidines using resin-bound isothiourea building blocks and multidirectional resin cleavage.

A series of pharmacologically active, functionalized 4-aryl-3,4-dihydropyrimidine-5-carboxylates (DHPMs) are prepared by a versatile novel solid phase approach. In the key step, a polymer-bound thiouronium salt is condensed with unsaturated 1-ketoesters. The resulting polymer bound 1,4-dihydropyrimidines are cleaved from the resin employing multidirectional resin cleavage strategies.

Determination of absolute configuration in 4-aryl-3, 4-dihydro-2(1H)-pyrimidones by high performance liquid chromatography and CD spectroscopy.

The absolute configuration of three 4-aryl-3, 4-dihydro-2(1H)-pyrimidones (Biginelli compounds, DHPMs) was established by comparison of the typical circular dichroism (CD) spectra of individual enantiomers with reference samples of known absolute configuration. The enantiomers were obtained by semipreparative separation of racemic mixtures on a Chiralcel OD-H chiral stationary phase. The method was used to establish the enantiopreference of various lipases in biocatalytic kinetic resolution experiments employing activated DHPM esters.

Dipolar Cycloaddition Reactions of Dihydropyrimidine-Fused Mesomeric Betaines. An Approach toward Conformationally Restricted Dihydropyrimidine Derivatives(1).

The bimolecular and intramolecular cycloaddition potential of various 4-aryldihydropyrimidine-fused mesomeric betaines was investigated. Dihydropyrimidine-fused isothiomünchnones and isomünchnones were found to undergo 1,3-dipolar cycloaddition reactions with electron-deficient dipolarophiles such as DMAD, methyl propiolate, methyl vinyl ketone, or N-methylmaleimide. In contrast, cross-conjugated mesomeric thiazinium betaines underwent 1,4-dipolar cycloaddition reaction with electron-rich dipolarophiles such as ynamines or ketene acetals.

Studies Dealing with the Cycloaddition/Ring Opening/Elimination Sequence of 2-Amino-Substituted Isobenzofurans.

The alpha-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.

A Facile and Efficient Synthesis of Thieno[2,3-c]furans and Furo[3,4-b]indoles via a Pummerer-Induced Cyclization Reaction.

The alpha-thiocarbocation generated from the Pummerer reaction of an o-heteroaroyl-substituted sulfoxide is intercepted by the adjacent keto group to produce an alpha-thio-substituted heteroaromatic isobenzofuran. In the presence of a suitable dienophile, the reactive o-xylylene undergoes a Diels-Alder cycloaddition followed by an acid-catalyzed ring-opening and aromatization to give heteroaromatic naphthalene derivatives. This one-pot procedure occurs smoothly with electron-deficient dienophiles.

Tandem Pummerer-Diels-Alder Reaction Sequence. A Novel Cascade Process for the Preparation of 1-Arylnaphthalene Lignans.

The alpha-thiocarbocation generated from the Pummerer reaction of an o-benzoyl-substituted sulfoxide is intercepted by the adjacent keto group to produce an alpha-thio isobenzofuran as a transient intermediate which undergoes a subsequent Diels-Alder cycloaddition with added dienophiles. Acid-catalyzed ring-opening of the cycloadduct followed by aromatization gave an arylnaphthalene derivative. With acetylenic dienophiles, the tandem cyclization-cycloaddition sequence provided tetralones which result from a pinacol-type rearrangement of the primary cycloadducts.

Ultrastructure of Kolmer's crystalloid in the pinealocytes of the common spiny mouse (Acomys cahirinus dimidiatus).

Light- and electron-microscopical observations revealed a rod-like inclusion body in the pinealocytes of the common spiny mouse (Acomys cahirinus dimidiatus). Ultrastructurally, the body is composed of a varying number of tubes whose wall consists of thin filaments aligned in helical arrangement. The inner and outer surface of the wall is covered with ribosome-like granules.

Cross-conjugated and pseudo-cross-conjugated mesomeric betaines, XVIII: Bicyclic mesoionic pyrimidines with cardiovascular activity.

Reaction of alpha-Anilino-azines 1a-i with activated malonates (magic malonates) 2a-e leads to bicyclic mesoionic systems 3-7. Out of these, pyrimido[1,2-alpha]pyrimidines 3b,d are active as cardiotonics, whereas pyrimido[1,2-alpha]pyrimidines 4a-g show significant anti-anginal and anti-hypertensive activity.