Topic
Bicyclic molecule
About: Bicyclic molecule is a research topic. Over the lifetime, 29587 publications have been published within this topic receiving 451252 citations. The topic is also known as: bicyclic molecule.
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TL;DR: Semiempirical calculations indicate that the thermodynamic stabilities of the three alternative isomeric ring systems are similar to that of the classical penam or penem structure, and ab initio methods suggest that the N-fused bicyclic β-lactams are considerably more electrophilic than the corresponding C-fusion compounds.
Abstract: Described in this article are studies of structurally novel [3.2.0]bicyclic β-lactam ring systems that are isomeric to those of the penicillin, penem, and clavulanic acid families of antibiotics, but which have the lactam functionality arranged in alternative orientations within the four-membered ring. Semiempirical calculations indicate that the thermodynamic stabilities of the three alternative isomeric ring systems are similar to that of the classical penam or penem structure, and ab initio methods reveal that the LUMO energies of the two C-fused ring structures 11 and 12 are more than 1 eV lower than that of 2-azetidinone, but 0.22 to 0.73 eV higher than that of the penem ring 13. The LUMO energy of the N−S fused penem structure 14 is about 0.2 eV lower than that of 13. These studies also suggest that the N-fused bicyclic β-lactams are considerably more electrophilic than the corresponding C-fused compounds. Several of the new heterocyclic rings were synthesized using a two-step cyclization strategy t...
88 citations
88 citations
TL;DR: The chiral auxiliaries of the cyclized products obtained were efficiently removed by the novel manganese dioxide oxidation under remarkably mild conditions, and the method was successfully applied to the formal synthesis of optically active 20-epiuleine.
Abstract: Highly stereoselective asymmetric 6π-azaelectrocyclization was achieved with generality, based on the reaction between the (E)-3-carbonyl-2,4,6-trienal compounds and the (−)-7-alkyl-cis-1-amino-2-indanol derivatives as the effective novel chiral amines. Furthermore, the chiral auxiliaries of the cyclized products obtained were efficiently removed by the novel manganese dioxide oxidation under remarkably mild conditions, and the method was successfully applied to the formal synthesis of optically active 20-epiuleine.
88 citations
TL;DR: In this paper, a chiral hydroperoxy alcohol TADOOH (={(4R,5R)-5-[(hydroperoxydiphenyl)methyl]-2,2-dimethyl-1,3-dioxolan-4-yl}diphenynylmethanol) was tested as chiral oxidant in three types of reactions: the epoxidation of enones with base catalysis (Scheme 2), the sulfoxidation, and the Baeyer-Villiger oxidation of bicyclic and tricy
Abstract: Replacement of one OH group in TADDOL (=α,α,α′,α′-tetraaryl-1,3-dioxolane-4,5-dimethanol) by an OOH group gives a stable, crystalline chiral hydroperoxy alcohol TADOOH (={(4R,5R)-5-[(hydroperoxydiphenyl)methyl]-2,2-dimethyl-1,3-dioxolan-4-yl}diphenylmethanol) 3, the crystal structure of which resembles those of numerous other TADDOL derivatives (Fig. 2). The new hydroperoxide was tested as chiral oxidant in three types of reactions: the epoxidation of enones with base catalysis (Scheme 2), the sulfoxidation of methyl phenyl sulfide (Scheme 3), and the Baeyer-Villiger oxidation of bicyclic and tricyclic cyclobutanones, rac-10a – d with kinetic resolution (Scheme 4, Fig. 3, and Table). Products of up to 99% enantiomer puritiy were isolated (the highest values yet observed for oxidations with a chiral hydroperoxide!). Mechanistic models are proposed for the stereochemical courses of the three types of reactions (Schemes 5 and 6, and Fig. 4). Results of AM1 calculations of the relative transition-state energies for the anionic rearrangements of the exo Criegee adducts of TADOOH to the enantiomeric bicyclo[3.2.0]heptan-6-ones are in qualitative agreement with the observed relative rates (Table and Fig. 5).
88 citations
TL;DR: Readily accessible hex-5-ynylidenecyclopropane derivatives cycloisomerize to bicyclic five-membered carbocycles upon heating with catalytic amounts of a palladium complex.
Abstract: Readily accessible hex-5-ynylidenecyclopropane derivatives cycloisomerize to bicyclic five-membered carbocycles upon heating with catalytic amounts of a palladium complex.
88 citations