Asymmetric Sequential Allylic Transfer Reaction for the Synthesis of 2-(1-Stannylvinyl)-1,3-diols: Concise Synthesis of (−)-Avenaciolide and (−)-Isoavenaciolide

Synthesis of (+)-Hypoxylactone through Allenoate γ-Addition: Revision of Stereochemistry

A synthesis of (+)-hypoxylactone has been accomplished in four steps starting from the allenoate γ-addition of threo-3-chloro-2-silyoxybutanals, leading to the revision of stereochemistry. The key was the discovery of control elements required to matching/mismatching cases in the allenoate γ-addition to provide the desired adducts as a single isomer. The utility of the γ-adduct was demonstrated with the Au(I)-catalyzed cyclization to afford (+)-xylogiblactone A. Use of Ag₂O was the key to epoxidation for preventing epimerization of the γ-lactone ring.

Asymmetric palladium-catalyzed umpolung cyclization of allylic acetate-aldehyde using formate as a reductant

Asymmetic palladium/chiral diphosphine-catalyzed umpolung cyclization of allylic acetate-aldehyde using formate as a reductant affordscis-disubstituted pyrrolidine, tetrahydrofuran, and spiro carbocycle.

Regulation of diastereoselectivity in the carbocyclization of allenyl (S)-N-tert-butylsulfinimines through a three-component assembly

Allenyl sulfinimines can be stereoselectively cyclized with hexamethylditin under palladium catalysis conditions followed by a selection of additives for an activated transmetalation. Reactivity and diastereoselectivity for the cyclization strongly depend on the characteristics of additives. A highly diastereoselective synthesis of five-membered rings is achieved from the reaction of the corresponding allenyl (S)-N-tert-butylsulfinimies through the following sequence. After the distannylation of the allenyl group with hexamethylditin catalyzed by the Pd complex, stereochemical routes are additive dependent: addition of SnCl4 affords a cis ring exclusively, whereas a trans ring is formed predominantly by the introduction of B-bromocatecholborane. Extension of the methodology to the synthesis of six-membered cis rings is achieved by using B-bromocatecholborane. Stereochemical relationships of products were unambiguously deduced by X-ray crystallography.

Free radical 5-exo-dig cyclization as the key step in the synthesis of bis-butyrolactone natural products: experimental and theoretical studies

Radical cyclization reactions were performed by 5-exo-dig mode to yield cis-fused bicyclic systems, leading to the synthesis of bis-butyrolactone class of natural products. The study was aimed at understanding the impact of alkyl side chains of furanoside ring systems in L-ara configuration on the radical cyclization. It was amply demonstrated by experimental studies that the increase in the length of the alkyl side chain has an effect on the cyclization: while efficient cyclization reactions could be realized with methyl and ethyl side chains, the yields were significantly reduced in the case of n-pentyl side chain. Theoretical studies using DFT and (RO)MP2 methods were carried out to analyze the influence of the substitution pattern on the cyclization barriers.

Differential use of anhydropyranosides for enantiopure routes to bis-gamma-butyrolactones: a new approach to the frameworks of antibiotic and anticancer agents isoavenaciolide and ethisolide

Regio- and chemoselective syntheses of enantiopure bis-furanoids are described. These compounds are chirons for several families of bioactive natural products, including isoavenaciolide and ethisolide. Reaction of a 3,4-epoxy pyran with beta-ketoester dianions delivers substituted pyranosides in high yield. Cyclization then yields fused furan-pyran intermediates. Oxidation, deprotection, and rearrangement lead to bis-furanoids that bear the essential framework and stereochemistry of ethisolide and isoavenaciolide.

A diastereoselective carbocyclisation of allene-hydrazones through the intramolecular allylic transfer reaction

A diastereoselective synthesis of cyclic hydrazines was achieved from a carbocyclisation of allene-hydrazones by the Pd-catalyzed distannylation of an allene moiety, followed by the transmetallation of allylic stannane intermediates with TiCl4.

Olefin Metathesis of the Aligned Assemblies of Conjugated Polymers Constructed through Supramolecular Bundling

The ordered structures constructed from an aligner molecule 1o and conjugated polymers (CPs) were efficiently converted into the poly-pseudo-rotaxane structures by the template-assisted ring-closing olefin metathesis (RCM) of olefinic groups at the peripheral positions of 1o. Moreover, the poly-pseudo-rotaxane structures permitted the separation of the crystalline ordered assemblies of CP by size exclusion chromatography and the preservation of the sheet morphologies after the treatment with trifluoroacetic acid. The morphologies and the periodicities of assemblies were also maintained after the retrieving treatments.

exTTF as a Building Block for Fullerene Receptors. Unexpected Solvent-Dependent Positive Homotropic Cooperativity

The first exTTF-based receptor for molecular recognition of fullerene is described. Unexpectedly, the receptor shows completely different binding modes in chlorobenzene and CHCl3/CS2 mixtures. In the aromatic solvent, the receptor binds C60 in a noncooperative fashion (nH = 1) with a Kassoc = (2.98 +/- 0.12) x 103 M-1, whereas in CHCl3/CS2 mixtures, it shows a marked positive homotropic cooperative effect (nH = 2.7) toward binding of C60, with an apparent binding constant of (3.56 +/- 0.16) x 103 M-1. The unique solvent-switchable behavior of our receptor might find use in the controlled self-assembly of exTTF-C60 donor-acceptor ensembles.