Synthesis of fused bicyclic glutarimides

We describe an efficient route towards the synthesis of fused bicyclic glutarimides using facile [3+3] reaction of α-sulfonylacetamides with different α,β-unsaturated esters as the key step. Intramolecular cyclization of 4-substituted 3-sulfonylglutarimide to form 5,6-, 6,6- or 6,7-fused bicyclic glutarimides was accomplished via alkylation, oxidative cyclization or ring-closing metathesis in modest yield.     

Palladium-catalyzed tandem Heck and aldol reactions between 2-bromobenzaldehydes and functionalized alkenes leading to naphthalenes

2-Bromobenzaldehydes react with an array of suitably functionalized alkenes in the presence of a catalytic amount of a palladium catalyst together with a base to afford the corresponding naphthalenes in moderate to good yields.     

Design and synthesis of novel polyheterofunctionalyzed cyclopentenones

Novel highly functionalized chlorocyclopentenones derivatives with N-, O-, and C-substituents were synthesized.     

A novel palladium-catalyzed dicarbonylation process leading to coumarins

A novel approach to coumarin derivatives has been developed starting from readily available 2-(1-hydroxyprop-2-ynyl)phenols, based on an unprecedented palladium-catalyzed dicarbonylation process. Reactions were carried out in the presence of catalytic amounts of PdI2 in conjunction with an excess of KI in MeOH as the solvent at room temperature and under 90 atm of CO to give 3-[(methoxycarbonyl)methyl]coumarins in good to high isolated yields (62-87%).     

Four-component tandem protocol for the stereoselective synthesis of highly functionalized [1,4]-thiazines

The one-pot, four-component tandem reaction of ethyl 2-[(2-oxo-2-arylethyl)sulfonyl]acetate/ethyl 2-[(2-ethoxy-2-oxoethyl)sulfonyl]acetate, an aromatic aldehyde and pyrrolidine provides a rapid and facile access to new ethyl 3-aroyl-1-benzyl-2,2-dioxo-4-aryloctahydro-2-pyrrolo[2,1-c][1,4]thiazine-1-carboxylates/diethyl 1-benzyl-2,2-dioxo-4-aryloctahydro-2-pyrrolo[2,1-c][1,4]thiazine-1,3-dicarboxylates. This reaction shows high stereoselectivity and proceeds in good yields.     

A novel enzymatic tandem process: utilization of biocatalytic promiscuity for high stereoselective synthesis of 5-hydroxyimino-4,5-dihydrofurans

A lipase-catalyzed protocol for the synthesis of 5-hydroxyimino-4,5-dihydrofurans via tandem coupling between β-nitrostyrenes and 1,3-dicarbonyl compounds was developed in a ‘one-pot’ strategy. A series of β-nitrostyrenes were employed to expand the scope of this new biocatalytic promiscuity with high stereoselectivity (Z/E up to 99:1) and moderate to good yields. The reaction activity of 1,3-cyclohexanedione was found to be better than linear 2,4-pentanedione, while ethyl acetoacetate and diethylmalonate were not suitable for this reaction under the same conditions. Single-crystal X-ray diffraction analysis indicated that the reaction was stereoselective and Z-stereomer was found to be the major product. A reaction mechanism was supposed to elucidate the biocatalytic process.     

A diastereoselective tandem RCM approach to spiropiperidines

This paper outlines the stereocontrolled synthesis of a functionalised spiropiperidine through a diastereoselective tandem RCM reaction. The diastereoselectivity of this process was found to be strongly dependant on the nature of the catalyst; the less active first generation Ru-carbene complexes provided the desired spirocycle in high yield and with good stereocontrol. Additionally, the further functionalisation of the spiropiperidine was carried out through a regio- and stereoselective dihydroxylation reaction employing Donohoe's OsO₄-TMEDA conditions.     

A tandem oximation-cyclization route to Δ-isoxazolines

3,5-Disubstituted Δ²-isoxazolines can be prepared from the corresponding β,γ-unsaturated ketones by treatment with hydroxylamine hydrochloride and sodium hydroxide. Evidence indicates that the mechanism of this reaction involves the formation of three intermediates; oximation of the ketone, rearrangement of the alkene, and intramolecular Michael addition of the resulting α,β-unsaturated oxime.     

An efficient organocatalytic method for tandem synthesis of functionalized 2-pyridones

Highly functionalized 2-pyridones are obtained via a tandem reaction between primary amines and acetylenic esters in the presence of N-methylimidazole as an organocatalyst.     

Divergent syntheses of L-733, 060 and CP-122721 from functionalized pieridinones made by one-pot tandem cyclization

An efficient diastereoselective approach to access trans-5-hydroxy-6-substituted 2-piperidinones skeleton has been developed through one-pot intramolecular tandem process of O-benzyl protected aldimine 11 with Grignard reagents. The diastereoselectivity of substitution at C-6 position of 2-piperidinone was controlled by α-benzyloxy group. In addition, the utility of this straightforward cascade process is demonstrated by the asymmetric syntheses of (+)-L-733, 060 (2) and its 2-substituted analogue 3, as well as (+)-CP-122721 (5).     

A tandem enyne/ring closing metathesis approach to the synthesis of novel angularly fused dioxa-triquinanes

Triquinanes and their oxygenated congeners, oxa- and dioxa-triquinanes, exhibit versatile biological activities in conjunction with synthetically challenging molecular architecture. Owing to these properties, several new strategies have been developed to accomplish the synthesis of these sesquiterpenes. Among the new strategies, cascade radical cyclization strategy has been broadly explored and well studied. Herein, we report our efforts in detail for the synthesis of dioxa-triquinanes using a domino enyne/RCM strategy as the key step. Carbohydrate based synthesis not only allows the use of inexpensive and optically pure starting materials, but also the furanose derivatives, which already possess one of the requisite dihydro-furan moieties in the desired dioxa-triquinane. The other two five-membered rings were constructed simultaneously by the cascade enyne/RCM reaction using the Grubbs' second-generation catalyst. During the course of our synthesis it was observed that the acetonide protection hinders the RCM reaction, after the initial enyne metathesis reaction. The reaction underwent smoothly under argon atmosphere, whilst use of ethylene atmosphere was found to hinder the formation of the tandem enyne/RCM product. The effect of substitution on the key reaction is described here.     

First example of base-promoted tandem alkylation-bromination of 2-bromothiophene via halogen dance process: a remarkable temperature effect

Metalation-alkylation of 2-bromothiophene 1 when conducted at low temperature led to the 5-alkylated 2-bromo products 2. While, at room temperature, the same sequential reactions afforded the original dibromo-alkylated thiophenes 3 following an unprecedented halogen transfer-based halogen dance process in highly regiocontrolled and ordered way.     

A tandem reaction of 2-acetylmethylene-1,3-dithiolanes via fragmentation of the dithiolane ring in the presence of amines: a facile route to functionalized thioamides

A facile and efficient route to functionalized thioamides has been developed by a tandem reaction of 2-acetylmethylene-1,3-dithiolanes via fragmentation of the dithiolane ring upon heating and in the presence of an amine.     

A highly regioselective tandem 1,3-dipolar cycloaddition of cyclopropene 1,1-diesters and nitrile oxides: synthesis of highly functionalized isoxazoles

A highly regioselective tandem 1,3-dipolar cycloaddition of cyclopropene 1,1-diesters with nitrile oxides was described. This reaction supplied a new method for synthesis of polyfunctionalized isoxazole derivatives in moderate to excellent yields under mild conditions.     

A novel Ireland-Claisen rearrangement/Diels-Alder tandem reaction of propargylic acrylates with acyclic dienophiles

A novel DABCO-catalyzed Ireland-Claisen rearrangement/Diels-Alder tandem reaction of propargylic acrylates 3 with dienophiles 4 was developed in the presence of an excess TMSCl and DBU with 1% hydroquinone as polymerization inhibitor in acetonitrile at refluxing temperature under air.This protocol gave cyclicα,β-unsaturated carboxylic acids 5 with complete regioselectivity.     

A facile tandem protocol for the regioselective synthesis of novel thienobenzothiazepines

A series of new 3-benzyl-1,10-diaryl-4H,10H-thieno[3,4-c][1,5]benzothiazepines has been synthesised regioselectively from the reaction of 5-aryl-2,4-bis(arylmethylidene)dihydro-3-thiophenones with o-aminothiophenol in the presence of acetic acid. This transformation presumably occurs via a tandem Michael addition-condensation-isomerisation sequence.     

Organocatalyzed tandem process involving asymmetric protonations as a stereo-defining step

Enantioselective protonation reactions of enolates, enols, enol ethers, or enol esters have been extensively studied. On the other hand, their applications in tandem or cascade sequence have not been fully explored and examples of such reactions employing organocatalysts are few. This account describes some of the most common synthetic strategies recently developed to address such challenge.     

Synthesis of vinylcyclopentanes via samarium(II) mediated tandem reactions

In the presence of either visible light or HMPA, SmI₂ reacts with some carbohydrate derived ω-iodoallylic alcohols, and their acetylated derivatives, to give vinylcyclopentanediol and vinylcyclopentanetriol derivatives.     

A novel four-component tandem protocol for the stereoselective synthesis of highly functionalised thiazoles

The reaction of bis(aroylmethyl) sulfides with aromatic aldehydes and ammonium acetate in 1:2:1 molar ratio under solvent-free microwave irradiation afforded predominantly a series of thiazoles, viz., 1-aryl-2-[5(Z)-5-arylmethylidene-2,4-diaryl-2,5-dihydrothiazol-2-yl]ethanones stereoselectively. This reaction presumably occurs via a Knoevenagel condensation-Michael addition-cyclocondensation-ring opening-ring closing Michael addition sequence. The intermediacy of (Z,Z)-2,2′-thiobis(1,3-diarylprop-2-en-1-ones) in the above transformation is demonstrated by their conversion to the thiazoles upon reaction with ammonium acetate under solvent-free microwave irradiation.     

Iodine-mediated electrophilic tandem cyclization of 2-alkynylbenzaldehydes with anthranilic acid leading to 1,2-dihydroisoquinoline-fused benzoxazinones

An efficient iodine-mediated electrophilic tandem cyclization of substituted 2-alkynylbenzaldehydes with anthranilic acids under basic medium leading to iodo-1,2-dihydroisoquinoline-fused benzoxazinones is presented. Success of the protocol for the reaction of substituted 2-alkynylbenzaldehydes with 2-aminobenzamides to furnish isoquinoline-fused quinazolinones is also described.