An effective one-pot synthesis of 5-substituted tetronic acids

An expeditious one-pot synthesis of 5-substituted tetronic acids from aldehydes and terminal conjugated alkyne as starting materials is described. The entire process embodies two consecutive chemical events: a catalytic domino reaction to build the 1,3-dioxolane scaffolds 5 and a two-step acid-catalyzed trans-acetalization-lactonization reaction to furnish the tetronic acid derivatives 6.     

A facile one-pot five-component synthesis of glycoside annulated dihydropyrimidinone derivatives with 1,2,3-triazol linkage via transesterification/Biginelli/click reactions in aqueous medium

Copper(I) promoted Huigsen 1,3-dipolar cycloaddition of terminal alkyne with azide is utilized as an efficient protocol for the one-pot five-component synthesis of glycoside annulated dihydropyrimidinone derivatives with 1,2,3-triazol linkage accomplished by tert-butyl β-ketoester, arylaldehyde, urea, propargyl alcohol, and glycosyl azide through the combination of transesterification and Biginelli reaction in aqueous medium. This protocol provides an access to generate scaffolds with molecular diversity from readily available starting materials.     

Tandem conjugate addition-elimination for the diastereoselective synthesis of 4E-alkenyl syn-1,3-diols

We have developed a tandem conjugate addition-elimination sequence for the diastereoselective synthesis of protected allylic syn-1,3-diols, starting from vinyl sulfones. The sulfonyl group was then reduced with sodium amalgam to furnish the E-olefin as the major isomer. This method was applied to the synthesis of a trisubstituted alkene modeling the C21-C25 fragment of Dolabelide C.     

Enantioselective Synthesis of cis-Decalins by Merging the Birch Reduction and Inverse-Electron-Demand Diels–Alder Reaction

Herein, we show that the combination of the Birch reduction of readily available anisole derivatives and the catalytic asymmetric inverse-electron-demand Diels–Alder reaction of 2-pyrones can serve as a powerful platform for the diverse synthesis of synthetically important cis-decalin scaffolds. Enabled by a well-modified chiral bis(oxazoline) ligand/Cu^II complex, a wide range of polysubstituted cis-decalin scaffolds with up to six contiguous stereocenters were generated efficiently. The synthetic potential of this method is demonstrated by the concise synthesis of the sesquiterpene (+)-occidentalol and a key intermediate for seven triterpenes. Mechanistic studies suggest the 1,3-cyclohexadienes formed in situ are the key intermediates, and efficient kinetic resolution occurs when C2- and/or C3-substituted 1,4-cyclohexadienes are utilized as substrates. DFT calculations elucidated that the Diels–Alder reaction proceeds in a stepwise fashion and revealed the origins of the stereoselectivities.     

A Convenient Synthesis of 2-Alkyl-mono-O-alkylated and 2-Alkyl Resorcinols

The title C, O -dialkylated resorcinols have seldom been prepared. We have developed a practical synthesis of this class of compounds starting with cyclohexane-1,3-dione. The key features of the synthesis are mono-O-alkylation of a 2-alkyl cyclohexane-1,3-dione and Pd-C catalyzed or NBS/DBU annuitization of the resultant O-alkyl-2-alkyl cyclohexane-1,3-dione. The use of cyclohexane-1,3-dione allows regioselective alkylations that would not be possible with resorcinol itself. A convenient synthesis of 2-alkyl resorcinols from cyclohexane-1,3-dione has also been achieved.     

An alternative stereoselective synthesis of greensporone C

Greensporone C, a new 14-membered resorcylic acid lactone, has been synthesized from inexpensive and commercially available starting materials. This convergent synthesis utilizes Cross metathesis using the Grubbs Hoveyda catalyst, alkylation of 1,3-dithiane and Yamaguchi macrolactonization as key steps.     

Fused-s-triazino heterocycles. XII. 13H-4,6,7,8,13a, 13c-hexaazabenzo-[de]naphthacene,a new ring system

The synthesis of the titled compound is described using 5-(2-carboxyanilino)-2-methyl-1,3-4,6,9b-pentaaza-phenalene as starting material.     

Structural analogues of quinoline alkaloids: Straightforward route to [1,3]dioxolo[4,5-c]quinolines with antibacterial properties

Compounds bearing [1,3]dioxolo-quinoline scaffolds have been found in quinoline-based natural products; the only exception is the [1,3]dioxolo[4,5-c]quinoline moiety with a rare occurrence in both natural and synthetic derivatives. In this article, we report the preparation of diversely substituted and functionalized [1,3]dioxolo[4,5-c]quinolines using [1,3]dioxolo[4,5-c]quinoline-4-carbaldehyde (DQC) as the common intermediate. DQC was synthesized on a large scale from anthranilic acid and chloroacetone as the starting materials, with the rearrangement of acetonyl-anthranilate as the key step. The developed method allows for the simple preparation of [1,3]dioxolo[4,5-c]quinolines with various C2 substituents on the quinoline scaffold. Additionally, the synthetic route was successfully applied to the preparation of 3-hydroxyquinoline-4(1H)-ones. The target compounds were tested against representative Gram-positive/negative bacteria, and two derivatives exhibited submicromolar minimum inhibitory concentrations against Micrococcus luteus.     

Synthesis of new 4-methyl-3-piperidones via an iron-catalyzed intramolecular tandem isomerization–aldolisation process

A new versatile synthesis of 3-piperidones is described, starting from amino acids. It uses, as a key step, an iron carbonyl-mediated intramolecular tandem isomerization–aldolisation reaction. These new heterocycles appear as useful scaffolds for the total synthesis of various types of bioactive molecules.     

Palladium- and copper-catalyzed synthesis of medium- and large-sized ring-fused dihydroazaphenanthrenes and 1,4-benzodiazepine-2,5-diones. control of reaction pathway by metal-switching

Methods for the synthesis of dihydroazaphenanthrene fused to macrocycles (2) and medium-ring heterocycles (4), as well as 1,4-benzodiazepine-2,5-diones (5), are developed. A distinctly different catalytic property of palladium and copper catalysts was uncovered that leads to the development of a divergent synthesis of two different heterocyclic scaffolds from the same starting materials, simply by metal-switching. Thus, starting from linear amide 3, palladium acetate triggers a domino intramolecular N-arylation/C-H activation/aryl-aryl bond-forming process to provide 4, while copper iodide promotes only the intramolecular N-arylation reaction leading to 5. In combination with the Ugi multicomponent reaction (Ugi-4CR) for the preparation of the linear amides, a two-step synthesis of either the 5,6-dihydro-8H-5,7a-diazacyclohepta[jk]phenanthrene-4,7-dione (4) or 1,4-benzodiazepine-2,5-diones (5), by appropriate choice of metal catalyst, is subsequently developed from very simple starting materials.     

A practical and scaleable total synthesis of the jaborandi alkaloid (+)-pilocarpine

The total synthesis of (+)-pilocarpine (as its nitrate salt) has been achieved in nine steps and 30% overall yield starting from racemic 2-(2′,2′-dimethoxyethyl)propane-1,3-diol, which was desymmetrised via an enzymatic protocol. A high yielding synthesis of a key α-ethylidene lactone precursor has been developed, which involves the palladium-catalysed decarboxylation/carbonylation of a 1,3-dioxan-2-one for formation of the γ-butyrolactone ring. Subsequent hydrogenation of the α-ethylidene lactone introduces the C(3)-stereochemistry to give a 72:28 mixture of (+)-pilocarpine and (+)-isopilocarpine, which are readily separable via recrystallisation of the (+)-pilocarpine nitrate salt.     

Synthesis of 2-Carbethoxy-1,3-butadiene irontricarbonyl starting from an electrophilic allene via a trimethylenemethane complex.

A new route starting from alkyl allenic esters for the synthesis of 1,3-butadiene irontricarbonyl complexes bearing a carbalcoxy group at position 2 is described and discussed.     

The Synthesis of 3-Acyl-2,3-dihydro-2,2-dimethyl-1,3-thiazoles

Acylation of 2,5-dihydro-2,2-dimethyl-1,3-thiazoles leads to 3-acyl-2,3-dihydro-2,2-dimethyl-1,3-thiazoles as potential starting materials for the total synthesis of racemic cephalosporins.     

Acid-Catalyzed Cyclodimerizations via Vinyl Cations as Intermediates

The electrophilic addition of hydrogen chloride and bromide to allene and of hydrogen bromide to methylacetylene at ?70 °C leads not only to the simple Markownikoff adducts but also to cis- and trans-1,3-dihalo-1,3-dimethylcyclobutanes. These cyclodimerizations, which evidently proceed via vinyl cations, have opened up new short routes for the synthesis of cyclobutane-, cyclobutene-, and bicyclobutane derivatives starting from substrates that are industrially readily accessible.     

Adamantyl-containing fluorinated 1,3-diketones

A convenient one-step procedure has been developed for the synthesis of fluorine-containing 2-(adamant-l-yl)-1,3-diketones by reaction of fluorinated 1,3-diketones with 1,3-dehydroadamantane. The products can be used as starting compounds for the preparation of new fluorinated adamantyl-containing heterocyclic compounds.     

PEG-assisted one-pot three-component synthesis of 1,3-oxazino quinoline and chromeno 1,3-oxazin derivatives under catalyst free condition

Abstract

A straightforward and greener PEG-assisted protocol has been disclosed for the cascade synthesis of [1,3]Oxazino quinoline, and chromeno[1,3]oxazin derivatives via three component reaction of multifarious aromatic amines with formaldehyde and 4-hydroxyquinoline-2(1H)-one or 4-methylumbelliferone by using very convenient reaction conditions. This methodology represents a sustainable approach for rapid access to a library of diversity oriented highly pure [1,3]oxazino scaffolds with broad substrate scope.     

Synthetic studies on (+)-biotin, part 15: A chiral squaramide-mediated enantioselective alcoholysis approach toward the total synthesis of (+)-biotin

An efficient stereocontrolled total synthesis of (+)-biotin (1) has been achieved via the intermediacy of Roche's lactone 5 starting from cis-1,3-dibenzyl-2-imidazole-4,5-dicarboxylic acid (2). The bifunctional cinchona alkaloid-derived squaramide-promoted enantioselective alcoholysis was utilizing as a tool for the construction of two contiguous stereocenters of C-3a and C-6a in biotin molecular with excellent enantioselectivity. In addition, the 4-carboxybutyl side chain was assembled by first using C4+C1 approach via a novel tricyclic thiophanium salt intermediate.     

Diastereochemical diversity of imidazoline scaffolds via substrate controlled TMSCl mediated cycloaddition of azlactones

[reaction: see text] We report herein a trimethylsilyl chloride mediated substrate controlled 1,3-dipolar cycloaddition for the diastereoselective synthesis of either syn- or anti-imidazolines. This method provides scaffolds with four points of diversity and control over two stereocenters.     

Facile DES-mediated synthesis and antioxidant potency of benzimidazoquinazolinone motifs

Research on Chemical Intermediates - One-pot multicomponent synthesis of benzimidazoquinazolinone scaffolds was achieved by reaction between 2-aminobenzimidazole, aldehyde, and 1,3-cyclohexadione...     

An Expedient Approach for the Synthesis of Bioactive Pyrazole,Isoxazole and Benzodiazepine‐Substituted Quinolin‐2(1H)‐one Derivatives

A sequence of functionalized pyrazole, isoxazole and benzodiazepine‐substituted quinolone derivatives were synthesized in good yield starting from readily available starting precursors. These approaches lead to the synthesis of hitherto unknown compounds with a varied substitution pattern by both conventional and microwave‐assisted method. A good number of analogues were evaluated for their in vitro cytotoxicity against human cervical and colon cancer cell lines by MTT protocol. Almost all the selected compounds showed remarkable cytotoxic activities. Among them, compound 4g and 4i emerged as the most promising scaffolds. These scaffolds will be used for further molecular level studies.