Enantioselective, NHC-Catalyzed Annulations of Trisubstituted Enals and Cyclic N-Sulfonylimines via α,β-Unsaturated Acyl Azoliums

All aboard please! A new reaction of enals and cyclic sulfonylimines, as the nucleophiles(!), is the first highly enantioselective NHC-catalyzed annulation of trisubstituted enals. The catalytically generated α,β-unsaturated acyl azolium undergoes a reaction with the enamine tautomer of the imine via an aza-Claisen rearrangement as the key C?C bond-forming step. High yields and enantioselectivities were achieved using β-, α,β-, and β,β'-substituted enals.     

Stereoselective organocatalytic one-pot α,α-bifunctionalization of acetaldehyde by a tandem Mannich reaction/electrophilic amination

The first asymmetric organocatalyzed one-pot α,α-bifunctionalization of acetaldehyde with two different electrophiles is described. A diarylprolinol silyl ether-catalyzed reaction of acetaldehyde with an imine and di-tert-butyl azodicarboxylate affords syn-2,3-diaminoalcohols with excellent ee values of up to 98%. This methodology was successfully applied to the synthesis of a chiral α,β-diaminocarboxylic acid.     

Tandem reactions catalyzed by lanthanide iodides. Part 1: Tandem Mukaiyama-Michael iminoaldol reactions

Samarium diiodide, as well as lanthanide triiodides catalyze a one-pot procedure allowing to perform sequentially the Mukaiyama-Michael addition of a ketene silyl acetal on a cyclic α,β-unsaturated ketone, followed by the addition of a glyoxylic, aromatic or heteroaromatic imine. According to the nature of the silyl group the adducts resulting from this tandem process are isolated as ketones or as enoxysilanes. The presence of a coordinating group on the imine increases the rate of the reaction.     

Highly Stereoselective Tandem Pummerer Reaction/α-Hydroxy Imine Rearrangement of E.P. β-Sulfinylenamines

Abstract.

The highly stereoselective tandem Pummerer reaction/alpha;-hydroxy imine rearrangement of E.P. α-fluoroalkyl-β-sulfinylenamines affording chiral non-racemic fluoropyruvaldehydes N,S-ketals is described.     

The asymmetric synthesis of β-lactam antibiotics-v. Application of chiral α,β-epoxyimines in ketene-imine cycloaddition reactions leading to homochiral 3-aminoazetidinones.

Imines derived from chiral α,β-epoxyaldehydes have been shown to be useful chiral glyoxal imine synthons in the ketene-imine cycloaddition reaction. This process, which proceeds with high levels of reaction diastereoselection, affords enantiomerically pure cis-substituted 3-amino-4-alkylazetidinones in good yields.     

Asymmetric Michael addition of glycine imines via quaternary ammonium ion catalysis

The asymmetric Michael addition of glycine imine esters to simple α,β-unsaturated ketones via PTC is investigated. It is found that by employing 1 mol % of a chiral quaternary ammonium salt, derived from α-methylnaphthylamine in conjunction with Cs₂CO₃, high enantioselectivities can be obtained in conjugate additions involving simple alkylvinylketones.     

Asymmetric total synthesis of antileukemic sesquiterpene (+)-ivalin

The one-pot double alkylation reaction of a chiral α,β-unsaturated imine (6) with isopropenyl Grignard reagent followed by methyl iodide has been shown to proceed highly asymmetrically. Subsequent stereoselective transformation of the derived adduct (10) has culminated in a first asymmetric total synthesis of the optically pure eudesmane sesquiterpene (+)-ivalin (1).     

Asymmetric synthesis of β′-amino-α,β-enones via addition of α,β-unsaturated ketone-derived enolates to chiral N-phosphonyl imines

Efficient asymmetric Mannich addition reactions between α,β-unsaturated ketone derived enolates and N-phosphonyl imines were reported. These reactions could proceed smoothly for a variety of imine substrates with good (up to 96%) chemical yields and excellent diastereoselectivities (up to 98:2 dr). The method reported in this work provides an easy access to chiral β′-amino-α,β-enones.     

α,β-不饱和内酯的光化学反应研究进展

α,β-不饱和内酯的光化学反应可广泛应用于核苷、稠环生物碱、萜类、甾类等多种光学活性物质与天然产物的合成中.根据不同的反应类型,综述了2(5H)-呋喃酮等α,β-不饱和内酯的光化学1,4-加成反应、1,4-加成-并环反应、[2+2]环加成反应和复杂环加成反应的新进展.     

Brønsted acid-mediated annulations of pyrroles featuring N-tethered α,β-unsaturated ketones and esters: Total syntheses of (±)-tashiromine and (±)-indolizidine 209I

This study provides the first report of the construction of tetrahydroindolizines and tetrahydropyrrolo[1,2-a]azepines via Brønsted acid-mediated annulation of pyrroles featuring N-tethered α,β-unsaturated esters. In addition, the Brønsted acid-catalyzed cyclization of pyrroles featuring pendant α,β-unsaturated ketones was applied to complete total syntheses of the indolizidine alkaloids (±)-tashiromine and (±)-indolizidine 209I.     

Mukaiyama addition of (trimethylsilyl)acetonitrile to dimethyl acetals mediated by trimethylsilyl trifluoromethanesulfonate

(Trimethylsilyl)acetonitrile reacts smoothly with dimethyl acetals in the presence of stoichiometric trimethylsilyl trifluoromethanesulfonate (TMSOTf) to yield β-methoxynitriles. The ideal substrates for this reaction are acetals derived from aromatic aldehydes. Elimination to the corresponding α,β-unsaturated nitriles is observed as the major product in the case of electron-rich acetals. A mechanistic hypothesis that includes isomerization of the silylnitrile to a nucleophilic N-silyl ketene imine is presented.     

Organocatalytic asymmetric direct vinylogous Michael addition of α,β-unsaturated γ-butyrolactam to nitroolefins

The first organocatalytic enantioselective direct vinylogous Michael reaction of α,β-unsaturated γ-butyrolactam to nitroolefins is developed using cinchona alkaloids as the catalysts. Both product enantiomers are accessible with moderate to good enantioselectivity.     

Asymmetric phase-transfer-catalyzed conjugate addition of glycine imine to exocyclic α,β-unsaturated ketones: construction of polycyclic imines containing three stereocenters

We developed a facile, one-pot, multistep transformation between glycine imine and exocyclic α,β-unsaturated ketones in reactions catalyzed by chiral phase-transfer catalysts (PTC). A series of polycyclic imines containing three adjacent stereocenters were obtained in good to high yields with high diastereo- and enantioselectivities. Further transformation of the imines could afford N-fused polycyclic compounds with four adjacent stereocenters.     

The ruthenium catalyzed formation of chiral dihydropyrrolones from α,β-unsaturated imines: extending the reaction to terminal alkenes and investigating the formation of pyrroles as side-products

The reaction of α,β-unsaturated imines derived from cinnamaldehyde with CO and various alkenes produces chiral 1,3-dihydropyrrolone derivatives. As a byproduct the formation of 2,3-disubstituted pyrroles is observed in every reaction. If the imines are reacted with ethylene only, products with an ethyl group at C-3 of the imine chain are formed. The implications of these findings on the reaction mechanism are discussed.     

Bifunctional cinchona alkaloids-catalyzed asymmetric [4+2] cycloaddition reaction of β,γ-unsaturated α-keto esters with oxazolones

A highly enantioselective [4+2] cycloaddition reaction of β,γ-unsaturated α-keto esters with oxazolones was realized with readily available cinchona alkaloids as the catalysts. Using this reaction, a series of highly functionalized δ-lactones with adjacent α-quaternary-β-tertiary stereocenters were obtained in high yields (up to 97%) and with good-to-excellent enantioselectivities (up to 97% ee).     

Diastereoselectively switchable enantioselective trapping of carbamate ammonium ylides with imines

The diastereoselectively switchable enantioselective trapping of protic carbamate ammonium ylides with imines is reported. The intriguing Rh(2)(OAc)(4) and chiral Br?nsted acid cocatalyzed three-component Mannich-type reaction of a diazo compound, a carbamate, and an imine provides rapid and efficient access to both syn- and anti-α-substituted α,β-diamino acid derivatives with a high level control of chemo-, diastereo-, and enantioselectivity.     

{(COD)Ru[RNC(H)-C(H)C(Ph)]2} (RMe, Et): The first structurally characterized mononuclear ruthenium complexes with enyl-imino ligands and their relevance in ruthenium catalyzed C-H activation reactions

The reaction of α,β-unsaturated imines with [(1,5-cyclooctadiene)-bis(2-methylallyl)-ruthenium(II)] leads to the formation of mononuclear ruthenium complexes of the general formula {(COD)Ru[RNC(H)-C(H)C(Ph)]₂}. In these complexes the imine ligands are deprotonated in β-position with respect to the imine double bond and coordinate as an enyl-imino ligand. In the case of R = Me, Et the corresponding compounds have been characterized by X-ray crystallography. The relevance of these complexes with respect to ruthenium catalyzed C-C coupling reactions of the same α,β-unsaturated imines is demonstrated by the structural analysis of another mononuclear ruthenium complex in which two imine ligands are reductively coupled (R = Cy). [(1,5-Cyclooctadiene)-bis(2-methylallyl)-ruthenium(II)] also turns out to be a highly effective precatalyst in the reaction of the respective imines with carbon monoxide and ethylene to produce heterocyclic compounds.     

One-pot reactions of bicyclic zinc enolate generated from Ni-catalyzed reductive cyclization to furnish octahydro-4,7-ethanobenzofuran-9-one derivatives

The one-pot reactions of catalytically generated bicyclic zinc enolate with various electrophiles are reported. The zinc enolate as a key intermediate is efficiently delivered from Ni-catalyzed reductive cyclization of alkynyl cyclohexadienone. Employing aldehydes, imine, nitroalkene, and α,β-unsaturated carbonyl compounds as electrophiles, this new class of one-pot reactions gave multi-functionalized cis-hydrobenzofurans and octahydro-4,7-ethanobenzofuran-9-one derivatives in moderate to good yields.     

Applications of intramolecular diels-alder reactions of heterodienes. Facile syntheses of the heteroyohimbine alkaloids tetrahydroalstonine and akuammigine.

A facile, formal synthesis of the heteroyohimbine alkaloids tetrahydroalstonine (1) and akuammigine (2) has been completed in which the D/E ring system is constructed by the novel cyclization of the triene 10, a process which involves the intramolecular [4+2] cycloaddition of a heterodiene with an α,β-unsaturated amide.     

Alkaloide aus Cortex Condurango

From the CH₂Cl₂ extract of the bark of Marsdenia cundurango Reichenb. fil. (Cortex Condurango) a mixture of basic compounds could be isolated. Repeated thin layer and column chromatography yealded two alkaloids in pure form. For Kondurangamin A, which would be the mayor alkaloid with a content of 0.0007%, the structure was determined as 3β, 14β,20-trihydroxy-11 α-nicotinoyloxy-12β-acetoxy-5α,14β-pregnane and for Kondurangamin B as 3β,11α,12β,14β-tetrahydroxy-20-nicotinoyloxy-5α,14β-pregnane.