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.

Asymmetric Total Synthesis of Dendrobatid Alkaloids: Preparation of Indolizidine 251F and Its 3-Desmethyl Analogue Using an Intramolecular Schmidt Reaction Strategy

Abstract: Total syntheses of alkaloid 251F (1), a natural product detected from the skin extracts of the dendrobatid frog species Minyobates bombetes, and its racemic 3-desmethyl derivative (2) are reported. A Diels-Alder reaction initiated both syntheses and established four consecutive stereogenic centers. Important to the synthesis of 2 was a first-generation ozonolysis/olefination/aldol strategy to convert a [2.2.1] bicyclic acid to the [3.3.0]bicyclooctane diquinane 4b. Further elaboration to an appropriate keto azide allowed for a key intramolecular Schmidt reaction to deliver the tricyclic core of the target molecule. In a second-generation approach, a tandem ring-opening/ring-closing metathesis reaction effected an overall [2.2.1] --> [3.3.0] skeletal rearrangement to deliver diquinane 4a. In similar fashion, 4a was manipulated to an appropriate keto azide, and an intramolecular Schmidt reaction generated the core cyclic architecture of 251F.

Design, synthesis, and conformational analysis of a novel spiro-bicyclic system as a type II β-turn peptidomimetic

Abstract: A novel highly constrained spiro-bicyclic system (5) has been developed to mimic the type II β-turn, a secondary structural feature found in many bioactive peptides. This system simultaneously restricts three (Φ 2 , Ψ 2 , and Φ 3 ) of the four torsion angles that characterize the type II β-turn. As a test of the design, the asymmetric synthesis and conformational analysis of derivative 6 starting from (R)-2-allylproline is reported. Temperature dependent NMR chemical shift studies in CDCl 3 suggest that the amide proton of 6 is involved in an intramolecular hydrogen bond.Aso,NOE measurements place this hydrogen under the plane of the bicyclic ring system in proper proximity for this hydrogen bond to form with the acetyl carbonyl oxygen.Modeling studies of 6 produced eight minimum-energy conformations with torsion angles close to those of the classical type II β-turn.A comparison of the minimum-energy conformer of this molecule with the classical type II β-turn gave an RMS fit=0.161 A °

Regioselective synthesis of heterocycles containing nitrogen neighboring an aromatic ring by reductive ring expansion using diisobutylaluminum hydride and studies on the reaction mechanism

Abstract: A systematic investigation of the reductive ring-expansion reaction of cyclic ketoximes fused to aromatic rings with diisobutylaluminum hydride (DIBALH) is described. This reaction regioselectively afforded a variety of five- to eight-membered bicyclic heterocycles or tricyclic heterocycles containing nitrogen neighboring an aromatic ring, including indoline, 1,2,3,4,5,6-hexahydrobenz[b]azocine, 3,4-dihydro-2H-benzo[b][1,4]oxazine, 2,3,4,5-tetrahydrobenzo[b][1,4]thiazepine, 1,2,3,4,5,6-hexahydroazepino[3,2-b]indole, 2,3,4,5-tetrahydro-1H-benzothieno[2,3-b]azepine, 2,3,4,5-tetrahydro-1H-benzothieno[3,2-b]azepine, 5,6-dihydrophenanthridine, and 5,6,11,12-tetrahydrodibenz[b, f]azocine. The reaction mechanism leading to the rearrangement was investigated on the basis of the restricted Becke three-parameter plus Lee−Yang−Parr (B3LYP) density functional theory (DFT) with the 6-31G (d) basis set. It was found that the reaction proceeds through a three-centered transition state via a stepwise mechanism because th...

Carbon Cluster Cations with up to 84 Atoms: Structures, Formation Mechanism, and Reactivity.

Abstract: Carbon clusters are generated by laser desorption. Mass-selected beams are then pulse injected into an ion chromatography (IC) device. This device temporally and spatially separates the beam into its isomeric components. Arrival time distributions (ATDs) are then measured at the detector. From these distributions, accurate mobilities are obtained for each isomeric component, along with the the fractional abundance of each isomer. Different isomer structures are calculated using quantum chemical methods. A Monte Carlo technique uses these structures to obtain accurate theoretical mobilities. Comparison of theory with experiment allows unambiguous structural assignment of the various families of isomers present in the cluster beam. The results indicate that, for carbon cluster cations, linear structures exist up to C[sub 10[sup +]]. Several families of planar ring systems begin with monocyclic rings (ring I), which first appear at C[sub 7[sup +]], and persist beyond C[sub 40[sup +]]. Bicyclic rings (ring II) are first observed at C[sub 21[sup +]] and persist beyond C[sub 40[sup +]], followed by tricyclic rings (ring III, initiated at C[sub 30[sup +]]) and tetracyclic rings (ring IV, initiated at C[sub 40[sup +]]). A 3-dimensional family we label as 3-D rings begins at C[sub 29[sup +]], whose structure is not yet unambiguouslymore » assigned. This family never exceeds 5% of the ions at any cluster size. Finally, the first fullerene is observed at C[sub 30[sup +]], with this family dominating above C[sub 50[sup +]]. 32 refs., 14 figs., 4 tabs.« less