Metalated epoxides as carbenoids. Competing C-H and CC insertion in α-alkoxy epoxide systems

In a reinvestigation of the reactivity of carbenoids derived from epoxides, we studied the factors that could influence the chemoselectivity of the carbenoid insertion into vicinal C-H or CC bond in cyclic α-alkoxy epoxides bearing an alkenyl side chain. This reaction gives access to bi- or tricyclic systems, respectively.     

Acetal formation by solvolysis of glucal-derived donor-acceptor cyclopropanes

The conversion of glucal derived donor-acceptor cyclopropanes to acetals by TiCl₄ mediated ring opening and alcohol trapping is described. Good selectivity for the alpha anomer and yields near 90% are consistently observed with aliphatic, benzylic and allylic alcohols, phenols and thiophenols. The utility of this method to prepare oligosaccharides through intermediate O,S-acetals is illustrated.     

Direct oxidative functionalization of saturated dispiro-cyclopropanated bicyclo[3.3.1]nonanes

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New Dyes Based on Extended Fulvene Motifs: Synthesis through Redox Reactions of Naphthoquinones with Donor–Acceptor Cyclopropanes and Their Spectroelectrochemical Behavior

Novel dyes based on extended fulvene motifs are reported. The carbon skeleton was generated by a catalyzed addition of donor–acceptor cyclopropanes to naphthoquinone. The hydroxy group at the central ring of the tricyclic fulvene motif was converted into the triflate, which reacted efficiently with a wide range of nucleophiles, resulting in substitution and thereby providing new derivatives. The synthetic versatility allowed us to investigate the absorption, electrochemical, and UV/Vis-NIR spectroelectrochemical properties of these dyes as a function of the substituents. The dyes were shown to participate in reductive electrochemistry, the reversibility of which can be improved by appropriate selection of the substituents. Additionally, first signs of NIR electrochromism are presented, opening new avenues for the future investigations of such dyes.     

Nucleophilic ring opening of imidazolone activated donor–acceptor cyclopropanes with alcohols

Imidazolone-activated donor–acceptor cyclopropanes undergo alcohol-assisted ring opening under the co-action of p-toluenesulfonic acid. Under the optimized conditions, cyclopropanes and alcohols are coupled in 1,3-fashion with the retention of heterocyclic fragment. Substrates with aromatic donor groups provide the addition products in 75–99% yields as mixtures of two diastereomers.     

From Furan to Molecular Stairs: Syntheses,Structural Properties,and Theoretical Investigations of Oligocyclic Oligoacetals

The synthesis of oligocyclic oligoacetals using five‐membered rings as repetitive unit is described. Furan was used as the starting material, which is converted by a three‐step procedure consisting of twofold cyclopropanation, reduction, and oxidative ring enlargement into a tricyclic bis(enol ether). A repetition of this synthetic procedure leads to the formation of extended oligoacetal systems. Insights into the structures were gained by X‐ray crystallographic investigations and revealed helical arrangements of the subunits in the solid‐state. DFT (B3LYP) calculations have been carried out to elucidate the transition state of the ring enlargement and the flexibility of the annelated oligocyclic systems. Strain energies and topologies of potential cyclically condensed oligoacetals are predicted.     

推-拉电子体系环丙烷的不对称合成及其对映选择性开环/环化反应研究进展

含有推-拉电子(DA)体系的张力环化合物,例如DA环丙烷,是非常有用的合成砌块,被应用于天然产物全合成以及合成具有生物活性的分子的研究中。 近年来,本课题组利用手性铜、镍等配合物为催化剂,一方面发展了一系列高效合成手性DA环丙烷的新方法;另一方面陆续实现了仲胺、醇、硝酮、氮杂亚胺叶立德、烯醇硅醚、吲哚等多种亲核试剂与DA环丙烷的高对映选择性开环/环化反应。 本文结合我们课题组工作综述了DA环丙烷化合物的不对称合成、开环/环化反应以及动力学拆分方面的主要研究进展并进行了展望。