Recent Advances in Organic Reactions Catalyzed by Lanthanide(III) Complexes

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有机合成的新世纪――－有机合成近年进展鉴赏

本文简要介绍了2005年至今有机合成领域的进展,第一部份有机合成方法学的一些新进展中突出介绍了金属参与的有机合成反应、自由基介导的合成反应、"一个反应瓶"内的多步反应以及不对称反应四个方面;第二部份复杂天然产物全合成则以10个分子的为例介绍这方面的进展。     

Recent Advances in Organic Reactions Catalyzed by Lanthanide（Ⅲ） Complexes

Lanthanide compounds have been attracting much attention in organic synthesis.Chiral Ln-substituted BINOL have been widely studied in several asymmetric organic reactions.LnCl3 and Ln(OTf)3 have been expected to serve as Lewis acide and have been applied to many important synthetic reactions in a one-pot manner,Ln(O-i-Pr)3 exhibits some basic characters,which also can be utilized in some special organic transformation.This article deals with some lanthanides(Ⅲ）complexes promoted organic reactios,which we have recently developed.     

Ketone Synthesis by Direct,Orthogonal Chemoselective Hydroacylation of Alkenes with Amides: Use of Alkenes as Surrogates of Alkyl Carbanions

Direct functionalization of alkenes and direct transformation of carboxamides are two exciting areas that have attracted considerable attention in recent years. We report herein that secondary amides, the least reactive derivatives of carbonyl compounds, upon activated with triflic anhydride, can serve as effective hydroacylating reagents in partner with alkenes to yield ketones at ambient temperature. The method was applied to the one‐step synthesis of racemic dihydro‐ar‐turmerone. In this method, alkenes serve as surrogates of organometallic reagents, which allows the orthogonal chemoselective reactions. The ready availability of many olefins such as camphene and norbornene permits one‐step ketone synthesis that would require several steps by conventional methods.     

Synthesis and structure of hydroxyisoxazolidines and derivatives of hydroxylamine and alkenals

The reactions of N-substituted hydroxylamines with alkenals serve as a method for the synthesis of the corresponding 2-substituted 3(5)-hydroxyisoxazolidines. The reaction pathway is determined by the nature of the substituent attached to the nitrogen atom. Ring-chain isomerism has been detected in these newly obtained compoundsTranslated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1270–1276, September, 1987.     

Regio- and Stereoselective Thianthrenation of Olefins To Access Versatile Alkenyl Electrophiles

Herein, we report a regioselective alkenyl electrophile synthesis from unactivated olefins that is based on a direct and regioselective C−H thianthrenation reaction. The selectivity is proposed to arise from an unusual inverse-electron-demand hetero-Diels–Alder reaction. The alkenyl sulfonium salts can serve as electrophiles in palladium- and ruthenium-catalyzed cross-coupling reactions to make alkenyl C−C, C−Cl, C−Br, and C−SCF₃ bonds with stereoretention.     

Total Synthesis of (-)-α-Pinguisene

In previous work from our laboratory, we demonstrated that α-carbonyl radical cyclization reactions can serve efficiently as key steps in total synthesis of natural products.1 In this presentation,we report the total synthesis of (-)-α-pinguisene from enone 1 via α-carbonyl radical cyclization.     

Direct Trifluoromethylselenolation and Fluoroalkylselenolation of C−H Bonds: Recent Advances in Reagents Development and Reactions

Due to their high lipophilicity and strong electron-withdrawing property, more and more attention has been paid to introducing trifluoromethylseleno and fluoroalkylseleno moieties into organic molecules. In this short review, we categorize the synthesis of compounds that combine selenium and fluorinated moieties into two main types: trifluoromethylselenolation (CF₃Se) and fluoroalkylselenolation (R_fSe, except CF₃Se). This review aims to provide a summary of the recent advances in direct C−H trifluoromethylselenolation and fluoroalkylselenolation from the synthesis of trifluoromethylselenolation and fluoroalkylselenolation reagents to their application. Based on the method of how the R_fSe group was introduced, the main content is divided into three parts: transition-metal-free reactions, transition-metal-mediated/catalyzed reactions and photo-catalyzed reactions. The general substrate scope, mechanism and limitations would also be discussed so that we hope the review will serve as an inspiration for further research in this appealing research field.     

Stereoselective synthesis of vinylsilanes by a gold(I)-catalyzed acetylenic sila-cope rearrangement

Cationic tri-tert-butylphosphinegold(I) serves as a catalyst in the sila-Cope rearrangement of acetylenic allylsilanes. When phenol is employed as a nucleophile, the reaction allows for the stereoselective synthesis of vinylsilanes. Alternatively, use of methanol as a nucleophile leads to cyclic vinylsilanes, which can be viewed as latent vinylsilanes that are revealed on treatment with a mild Lewis acid. Thus, both of these reagents serve as useful reagents for stereoselective synthesis of trisubstituted olefins through transition-metal-catalyzed cross-coupling reactions.     

Synthesis of oligodeoxynucleotides using fully protected deoxynucleoside 3'-phosphoramidite building blocks and base recognition of oligodeoxynucleotides incorporating N3-cyano-ethylthymine

Oligodeoxynucleotide (ODN) synthesis, which avoids the formation of side products, is of great importance to biochemistry-based technology development. One side reaction of ODN synthesis is the cyanoethylation of the nucleobases. We suppressed this reaction by synthesizing ODNs using fully protected deoxynucleoside 3'-phosphoramidite building blocks, where the remaining reactive nucleobase residues were completely protected with acyl-, diacyl-, and acyl-oxyethylene-type groups. The detailed analysis of cyanoethylation at the nucleobase site showed that N3-protection of the thymine base efficiently suppressed the Michael addition of acrylonitrile. An ODN incorporating N3-cyanoethylthymine was synthesized using the phosphoramidite method, and primer extension reactions involving this ODN template were examined. As a result, the modified thymine produced has been proven to serve as a chain terminator.     

Sequential cyclization-elimination route to carbohydrate-based oxepines

A five-step preparation of carbohydrate-based oxepines from hept-1-enitols is presented. The hept-1-enitols were subjected to silyl protection and hydroboration/oxidation to give the protected heptan-1-itols. Swern oxidation of the homologated alcohols followed by sequential acetal formation/cyclization provided methyl 2-deoxyseptanosides that underwent elimination reactions to give the carbohydrate-based oxepines. The new sequence is an alternative to the ring-closing metathesis for the synthesis of carbohydrate-based oxepines from protected pyranose sugars. The product oxepines can serve as glycosyl donors in the synthesis of novel septanose carbohydrates. In addition, C-methylenealdehydo arabinofuranoside 16 was formed from 2-deoxyseptanoside 10 as the only product during protic acid mediated elimination reactions. This novel ring contraction complements other reported preparations of C-methylenaldehydo furanosides and underscores the acid-mediated reactivity introduced by competing eliminations between the C-1/C-2 and C-2/C-3 bonds.     

Aziridinofullerene: a versatile platform for functionalized fullerenes

An aziridine moiety on the fullerene core can serve as an acid-triggered reacting template for the controlled synthesis of a range of functionalized fullerenes that are otherwise difficult to synthesize in an efficient and selective manner. A copper-catalyzed aziridination of C(60) for the practical synthesis of aziridinofullerene 1 and acid-catalyzed reactions of 1 with mono- and bifunctional nucleophiles as well as alkynes are described. The rapid generation of structural diversity in a single chemical operation using the common platform 1 is notable.     

Recent Progress in Enzymatic Synthesis of Sugar Nucleotides

Glycosylation is one of the most important reactions in nature as it results in the formation of glycoconjugates with diverse biological functions. Sugar nucleotides serve as the natural donor molecules for the biosynthesis of such glycoconjugates and other carbohydrates. Furthermore, these donor molecules are also indispensable building blocks for the enzymatic synthesis of carbohydrates in vitro using Leloir-type glycosyltransferases. Given such importance, the biosynthetic pathways of sugar nucleotides have been exploited, enabling the development of both chemical and enzymatic approaches to produce these molecules. A survey of recent progress in enzymatic synthesis of common mammalian sugar nucleotides as well as their derivatives is thus presented. As a popular strategy, conjugation of sugar nucleotide synthesis with glycosyltransfer reactions and in vivo production of sugar nucleotides are also included.     

Regio‐ and Stereoselective Thianthrenation of Olefins To Access Versatile Alkenyl Electrophiles

Herein, we report a regioselective alkenyl electrophile synthesis from unactivated olefins that is based on a direct and regioselective C?H thianthrenation reaction. The selectivity is proposed to arise from an unusual inverse‐electron‐demand hetero‐Diels–Alder reaction. The alkenyl sulfonium salts can serve as electrophiles in palladium‐ and ruthenium‐catalyzed cross‐coupling reactions to make alkenyl C?C, C?Cl, C?Br, and C?SCF₃ bonds with stereoretention.     

Diversity through a branched reaction pathway: generation of multicyclic scaffolds and identification of antimigratory agents

A library of 91 heterocyclic compounds composed of 16 distinct scaffolds has been synthesized through a sequence of phosphine-catalyzed ring-forming reactions, Tebbe reactions, Diels-Alder reactions, and, in some cases, hydrolysis. This effort in diversity-oriented synthesis produced a collection of compounds that exhibited high levels of structural variation both in terms of stereochemistry and the range of scaffolds represented. A simple but powerful sequence of reactions thus led to a high-diversity library of relatively modest size with which to explore biologically relevant regions of chemical space. From this library, several molecules were identified that inhibit the migration and invasion of breast cancer cells and may serve as leads for the development of antimetastatic agents.     

Electrochemically active cross-linking reaction for fluorescent labeling of aliphatic alkenes

Although cross-linking reactions serve as a valuable tool for the integration of two or more functionalities or properties, the application of electrochemical synthesis to cross-linking reactions is restricted due to the difficulty of mass transfer. Thus, the primary purpose of this research is to explore electrochemical cross-linking systems to construct a fluorescent probe, triggered by the formation of a covalent linkage. The second purpose is to apply the probe to insoluble targets. Towards these goals, a combination of electrochemically active phenol derivatives and aliphatic alkenes were employed to form polycyclic compounds. Several of the dihydrobenzofuran derivatives formed through [3+2] cyclization reactions exhibited fluorescence. Furthermore, this approach allowed the effective modification of alkene-modified silica gel with electrochemically active species, which enables the construction of fluorescent probes that are triggered by C-C bond formation.     

A novel approach to the synthesis of amino-sugars. Routes to selectively protected 3-amino-3-deoxy-aldopentoses based on pyridinium salt photochemistry

A new approach for the synthesis of selectively blocked 3-amino-3-deoxyaldopentoses is presented. The strategy is based on employment of a pyridinium salt photocyclization-aziridine ring-opening sequence to prepare stereochemically defined, enantiomerically enriched aminocyclopentendiol derivatives. Ring-opening reactions transform these substances into terminally differentiated aminopolyols, which serve as precursors to the target amino-aldopentoses. The utility of this strategy is demonstrated by its application to the syntheses of protected derivatives of D- and L-3-amino-3-deoxyxylose, L-3-amino-3-deoxyarabinose, and a late-stage intermediate in a potential route to N-acetylneuraminic acid.     

VICARIOUS NUCLEOPHILIC SUBSTITUTION WITH SULFUR CONTAINING CARBANIONS

Abstract

Carbanions stabilized with sulfur containing substituents are versatile intermedi-ates in organic synthesis. The great value and importance of such carbanions is connected with specific properties of the sulfur atom which is capable to exist in a variety of valent states and to form many functional groups. These various sulfur-containing groups exert different carbanion stabilizing effects and can also serve as leaving groups in nucleophilic substitution or elimination reactions. Taking into account numerous types of sulfur containing functional groups and a variety of reactions they can promote, it is well understandable that reactions of sulfur-containing carbanions have been thoroughly studied and widely exploited in organic synthesis. The reactions of such carbanions with aliphatic electrophilic partners: alkylating agents, carbonyl compounds and Michael acceptors consist a major section of this field and were subject of numerous studies as well as many monographs.¹ Contrary to that, not very much was known about reactions of such carbanions with electrophilic aromatic compounds. Actually, there are only few reports on nitroarylation of sulfur-containing carbanions via replacement of halogen orfho- or para- to the nitro group in halonitrocornpounds.² There are also some reports on the alkylation of nitroarenes and heterocyclic compounds in the reaction with sulfonium3 and sulfoxonium4 ylides, dimethylsulfoxide carbanion,⁵ and dialkyl or alkyl aryl sulfones carbanions.⁶     

Asymmetric Michael Addition of Activated Alkenes to Nitro Alkenes Catalyzed by Organic Catalyst

Enantioselective Michael addition is one of the most powerfulbond-forming reaction in organic synthesis. [1] A mong the Michael acceptors, nitro alkenes are very attractive, because the nitro group is the most electron-withdrawing group known and it can serve as masked functionality to be further transformed after the addition has taken place. [2] Recently, asymmetric Michael reactions catalyzed by organic catalyst have draw much attention.[3]     

Heterocycle synthesis by copper facilitated addition of heteroatoms to alkenes, alkynes and arenes

The de novo synthesis of small organic heterocyclic molecules has benefited from recent protocols for copper-facilitated additions of heteroatoms to alkenes, alkynes and arenes. This tutorial review summarizes a number of these recent contributions. Copper salts can facilitate bond formations due to their ability to serve as Lewis acids, oxidizing agents and transition metal catalysts. The current understanding of the mechanisms of these reactions is presented. This review should be of interest to chemists involved in the synthesis of heterocycles and those investigating transition metal facilitated reactions.