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Biocatalysis has emerged as a powerful technology in recent years to synthesize clinically valuable molecules. In this context, hydrolases have been used to catalyse various organic transformations. Among hydrolases, α-amylase has been recognized as a valuable biocatalyst for chemical processing in a benign reaction environment. Further, it has been widely accepted in natural transformations like hydrolysis of starch as well as in non-natural transformations due to good selectivity, broad substrate scope, and good stability in organic solvents. Several significant organic transformations, such as the Aldol condensation, Hantzsch reaction, Mannich reaction, Knoevenagel condensation, Michael addition, and the multicomponent reaction catalyzed by α-amylase have been covered in this review. Further, the current review notes that α-amylase catalyses not only a single-step reaction but also multi-step and tandem non-natural transformations. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract A novel enantioselective Mannich reaction of γ -malonate-substituted α , β -unsaturated esters with N -protected arylaldimines was realized by using asymmetric phase-transfer catalysis (APTC). With amino acid-derived bifunctional thiourea-phosphonium salts as a catalyst, a series of enantio-enriched Mannich products could be synthesized under very mild and simple reaction conditions with high yields and enantioselectivities. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Abstract An efficient diastereoselective approach to access (4R)-hydroxy-(2S)-substituted methyl ketones pyrroles skeleton 4a-s has been developed through Mannich process involving N,O -acetal 6 and ketones and propionaldehyde in excellent yield with high diastereoselectivity (dr up to 99:1). In addition, the utility of this convenient Mannich process is demonstrated by the diastereoselective synthesis of Tuv fragment (2) and its analogue (18) of tubulysin V (1e). Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Abstract A highly stereoselective method for achieving the anti -Mannich reaction of aldehydes and ketones with ethyl (4-methoxyphenylimino)acetate was realized using the modularly designed organocatalysts (MDOs) self-assembled from cinchona alkaloid derivatives and (R)-pyrrolidien-3-carboxylic acid in the reaction media. The desired anti -Mannich products were obtained in good to excellent yields (up to 93%), excellent diastereoselectivities (up to 99:1 dr), and good to high enantioselectivities (up to 99% ee). Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Abstract A range of novel β-nitroacetamides with an alkenyl- or alkynyl tether were synthesized using the deprotonative or conjugate addition nitro-Mannich reaction. They were subjected to radical denitration-cyclisation with a 10 equivalent excess of tributyltin hydride, catalytic AIBN in refluxing benzene to explore the structural and electronic requirements for efficient cyclisation. Cyclisations of the β-nitroacetamides were successful in most cases, undergoing 5- exo -trig cyclisation to give the desired cyclopentyl or indanyl structures. Radical 1,4-translocation of a phenyl group was observed in several cases. Diastereoselectivity was low, with 2 or 3 of 4 possible diastereoisomers observed in most cases. Further purification by crystallisation allowed the isolation of some as single diastereoisomers. It was found that higher yields were obtained by increasing the substitution or reducing the degrees of freedom of the tether between the nitro group and the radical acceptor. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

A combination of an amino acid-derived chiral phosphine catalyst and methyl acrylate to catalyze the direct Mannich reaction of 3-substituted oxindoles and imines has been reported to afford 3-tetrasubstituted oxindole derivatives which are key structures for biological activities. The products are formed with a quaternary carbon and featured with two adjacent chiral centers. Various N -EDG(electron-donating group) and N -EWG(electron-withdrawing group) protected oxindoles, including 3-aryl and 3-alkyl substituted ones, have been evaluated with aromatic and aliphatic imines under this catalytic system, smoothly giving desired products in good yields as well as excellent diastereo- and enantioselectivities. [ABSTRACT FROM AUTHOR]

In this report, we try to show the importance of incorporation of name reactions in the sequential cascade reaction in which significantly decreasing the number of steps towards an ideal and practical multi-step synthesis of natural products as well showing virtually all the advantages already mentioned for “Click Chemistry”. In addition, since the chiral inductions are desired for most of these sequential name reactions, their asymmetric catalyzed reactions were also described. [ABSTRACT FROM AUTHOR]

7-Azaindoline amides are particularly useful in direct enolization chemistry due to their facilitated enolization in soft Lewis acid/Brønsted base cooperative catalysis. The Cu(I) complex of ( R , R )-Ph-BPE, a bis(tetrahydrophosphole)-type chiral bisphosphine ligand, exhibits consistently high catalytic performance and stereoselectivity irrespective of the nature of the α-substituent of the amides. Unexpectedly, however, alkyl-substituted bis(tetrahydrophosphole)-type ligands have substantially inferior catalytic performance. Evaluation of the optimized structures of Cu(I)/amide and Cu(I)/enolate complexes provided clues to dissecting the diverted reaction outcomes. [ABSTRACT FROM AUTHOR]

Regioselective reactions with supramolecular control are of great interest. Herein, the para -regioselectivity in the Mannich reaction of phenol with formaldehyde and dimethylamine was achieved with the use of β-cyclodextrin (β-CD), giving 4-( N , N -dimethylaminomethyl)phenol ( p -AP) as major product. 1 H NMR and ITC measurements of the binding of β-CD with the reactants and the products o - and p -AP revealed a new mechanism, in which β-CD includes p -AP instead of phenol to control the reaction regioselectivity. This product-inclusion mechanism is remarkably different to the known reactant-inclusion process. [ABSTRACT FROM AUTHOR]

The multicomponent Mannich reaction is a green and classical method for the preparation of β-aminoketones and β-aminoaldehydes (Mannich bases) and, as such, is one of the most important reactions in organic chemistry. The resulting Mannich bases are of particular interest due to their biological activity as well as their use as synthetic building blocks and precursors of valuable pharmaceuticals products. In this context, various elegant methods for multicomponent Mannich reactions have been developing over last years. This review updates these reactions, including naphthoquinone derivatives that possess varied and important biological activities and whose Mannich reaction has been little explored in the literature. [ABSTRACT FROM AUTHOR]

A combination of an amino-acid derived chiral phosphine catalyst and methyl acrylate has been employed to catalyze the direct Mannich reaction of α-aryl isocyanoacetate and N -Boc-aldimines efficiently. The loading of the catalyst could be as low as 0.5 mol% without compromise on the yield and enantioselectivity and the corresponding chiral adducts were obtained in excellent yields (up to 98%) and good enantioselectivities (up to 95%). [ABSTRACT FROM AUTHOR]

New naphth[1,3]oxazino-benzazepines and -thienopyridines were synthesized using a modified Mannich-type synthetic pathway by the reaction of 4,5-dihydro-3 H -benz[ c ]azepine or 6,7-dihydrothieno[3,2- c ]pyridine and different substituted aminonaphthols. Reaction conditions were optimized using microwave irradiation, with relatively short reaction times and a temperature of 80 °C. The formation of undesired naphthoxazine by-products made the separation/purification of the products challenging, therefore the reactions were repeated and systematically studied, starting from secondary and tertiary aminonaphthol derivatives, when the isolation of an ortho -quinonemethide structure occurred unexpectedly. Scope and limitations of its formation were also investigated. Conformational studies including ring inversion of a selection of the novel polyheterocycles were performed using NMR methods and supplementary DFT modelling. [ABSTRACT FROM AUTHOR]

Quaternary phosphonium ion-pair or a salt derived from amino acid has been developed to catalyze the Mannich-type reaction of α-substituted ethyl cyanoacetates and 2-(2-nitrophenyl) acetonitrile to N -Boc imines. Experiments shown that more active cyanoacetates could be catalyzed by the gentle phosphonium ion-pair catalysis, while 2-(2-nitrophenyl) acetonitrile as the substrate has to be activated by quaternary phosphonium salts and strong base. All the reactions gave the corresponding highly functionalized chiral β-amino nitriles products with good yields, high diastereo- and enantioselectivities in mild conditions. [ABSTRACT FROM AUTHOR]

Tests of antiproliferative activity of Mannich adducts of aromatic nucleophiles and a chiral bicyclic imine revealed a di- tert -butylphenol derivative as a promising compound for further exploration. To study the influence of substitution pattern and a configuration of stereogenic centers on the inhibition of cancer cell growth, a series of Mannich bases were obtained with a good to high diastereoselectivity from the reaction of the imine and three isomeric di- tert- butylphenols. Six new enantiopure adducts were isolated and fully characterized. Selected derivatives were shown to exhibit an interesting antiproliferative activity comparable to cisplatin. [ABSTRACT FROM AUTHOR]

We hereby report the biomimetic synthesis of three flavonoid alkaloids, namely 8-(2″-pyrrolidinon-5″-yl)quercetin, 6-(2″-pyrrolidinon-5″-yl)-(–)-epicatechin and 8-(2″-pyrrolidinon-5″-yl)-(–)-epicatechin. These known natural products were prepared via an acid-catalysed regioselective phenolic Mannich reaction involving the electrophilic attack of an N -acyliminium ion on the corresponding flavonoidal precursors. The products were purified by preparative HPLC. The reactions showed high C8-regioselectivity. The major isomers of the synthesized flavonoid alkaloids were further characterized in terms of their medicinal-chemical properties. [ABSTRACT FROM AUTHOR]

An enantioselective Mannich reaction of N -Boc aminosulfones with 3-methylbenzofuran-2 (3H)-ones catalyzed by a quinine-derived bifunctional phase transfer catalyst was developed, by which a series of chiral benzofuranones bearing adjacent quaternary and tertiary carbon centers were obtained in high yields (up to 96%) with good diastereoselectivities (up to >99:1) and enantioselectivities (up to 98%). [Display omitted] [ABSTRACT FROM AUTHOR]

The development of the stereoselective synthesis of vinyl halides plays an important role in organic chemistry. The multi-functionalized vinyl iodide is one of the most important intermediates in functional organic compounds. We investigated stereoselective iodo-aldol and iodo-Mannich reactions using γ-alkoxy-α,β-alkynyl ketones. Characteristic features of titanium tetraiodide involve iodination ability and moderate Lewis acidity, which are successfully used for the present stereoselective synthesis of multi-functionalized vinyl iodides. Furthermore, we have succeeded in the synthesis of a useful tetra-substituted furan, via a Sonogashira coupling of the vinyl iodide moiety. The factors to control diastereoselectivity of the iodo-aldol reactions are explained in terms of theoretical calculations. Consequently, the obtained activation free energy and reaction energy indicate the experimentally observed E / Z -selectivity. [ABSTRACT FROM AUTHOR]

Synthesis of the core skeletons of the polycyclic alkaloids lycopodine and porantherine has been accomplished employing as a key step an I ntramolecular A zide- O lefin C ycloaddition reaction (IAOC)/enamine addition/Mannich cascade reaction. Applying this methodology, the first synthesis of C 15 -desmethyl lycopodine has been developed. [ABSTRACT FROM AUTHOR]

An effective and facile method for the synthesis of N- substituted trihydroxypiperidine derivatives is described. The Mannich-type reaction of protected 5- O -tosylate pentoses with amines and ketones in the presence of p -TsOH provides convenient access to the stereoselective synthesis of N -substituted iminosugar C -glycosides as potential glucosidase inhibitors in good to excellent yields. [ABSTRACT FROM AUTHOR]

We developed a facile and practical synthesis of N -Boc-aminals, which can be used as precursors for less accessible N -Boc-imines. Aminals were obtained via simple dehydration condensation reactions of t -butyl carbamate (BocNH 2 ) and various aldehydes in acetic anhydride, followed by filtration and washing with hexane. The obtained N -Boc-alkynylaminals could be successfully applied in enantioselective Mannich-type reactions, catalyzed by chiral phosphoric acids, to afford optically active propargylamine derivatives. [ABSTRACT FROM AUTHOR]

New polydentate chiral ligands, containing the hydroxyl group, stereogenic sulfinyl group and enantiomeric prolinol moieties were synthesized and proved very efficient catalysts in the asymmetric diethylzinc addition to benzaldehyde, the asymmetric aldol condensation and the asymmetric Mannich reaction. Replacement of the central hydroxyl group with the second prolinol moiety of the same absolute configuration gave new ligands in which the sulfinyl group was not a stereogenic centre anymore, but which proved almost equally efficient as catalysts for the reactions investigated. The absolute configuration of the proline moiety exerted a decisive impact on the stereochemical outcome of these reactions, deciding about the absolute configuration of the products formed. [ABSTRACT FROM AUTHOR]

Reported herein is asymmetric synthesis of β-trifluoromethyl-β-amino acids via Mannich addition reactions between ( S s )- N -( tert -butanesulfinyl)-3,3,3-trifluoroacetaldimine and lithium enolates of alkyl acetates. In particular, the scope of this approach allows for preparation of the previously illusive, highly sterically constrained α,α-dialkyl-β-trifluoromethyl-β-amino acids. The method affords the target products with good to excellent chemical yields and diastereoselectivities. [ABSTRACT FROM AUTHOR]

The reactions of 1- or 2-naphthol, benzaldehyde or substituted benzaldehydes with tetrahydroisoquinoline, tetrahydrobenzo[ d ]azepine, tetrahydrobenzo[ c ]azepine or tetrahydrothieno[3,2- c ]pyridine under solvent-free conditions, allowed a series of tertiary aminonaphthols to be prepared. The reactions were accelerated by the use of microwave irradiation, and the yields were also improved. As an exception, the aminoalkylation of 2-naphthol with 1,2,3,4-tetrahydroisoquinoline in the presence of benzaldehyde led to the parallel N -alkylation and redox α-arylation of the tetrahydroisoquinoline in a ratio of 4:1. The reaction of 1-naphthol with 2,3,4,5-tetrahydro-1 H -benzo[ c ]azepine led to the formation of the N -alkylated compound as a single product, illustrating that the reaction route depends on the structures of the cyclic amine and the naphthol. [ABSTRACT FROM AUTHOR]

As part of our ongoing investigation into the synthetic application of nitroenamines several new densely substituted pyrimidine and pyrrolo-pyrimidine derivatives were prepared. Thus, 2-nitromethylenepyrrolidine and some open chain nitroenamines of phenyl-(2-nitro-1-phenyl-vinyl)-amine type were reacted with ethyl glyoxylate and a substituted aniline usually in a one-pot procedure to furnish the key intermediates for a subsequent cyclization. These compounds including a molecular fragment of 1,3-diamine type were subjected to a simple ring closure with formaldehyde to give the title compounds in good yields. The protocol reported has the advantages of mild reaction conditions, easy workup and inexpensive reagents. In an attempted removal of the 4-methoxy-phenyl protecting group from the 4-methoxy-phenyl substituted hexahydropyrrolo[1,2- c ]pyrimidine derivative, an unexpected periodic acid mediated ring cleavage and phenyl group migration was discovered. The structures of the synthesized new compounds were confirmed by spectral data, and, particularly, the hindered rotation and the unusual 1 H NMR characteristics of 4-(4-nitro-phenyl)-but-3-enoic acid ethyl ester derivative were discussed. [ABSTRACT FROM AUTHOR]

The powder of a crude extract from earthworms was used as a catalyst in three-component cascade Mannich-Michael reaction for the preparation of isoquinuclidine (azabicyclo[2.2.2]octane) derivatives. The influences of mole ratio of substrates, solvents, water contents, catalyst loading, temperature, and reaction time on the reaction were investigated. The developed system had excellent substrate adaptability. Various isoquinuclidines were obtained in yields of up to 99% with ratio of endo / exo of up to 76:24. This method provided a good example to use naturally existing catalyst for organic synthesis. [ABSTRACT FROM AUTHOR]

A highly enantioselective Mannich reaction of 3-substituted benzofuran-2(3 H )-ones and isatin N -Boc ketimines catalyzed by a chiral biscinchona alkaloid catalyst was developed, which proved to be an efficient way for the synthesis of chiral 3,3′-disubstituted benzofuran-2-one derivatives. The nucleophilic addition products were generally obtained in high yields (up to 99%) with very good diastereoselectivities (up to >95:5 dr) and enantioselectivities (up to 98% ee). [ABSTRACT FROM AUTHOR]

A range of chiral ester and chiral imide derivatives of 2-oxocyclohexanecarboxylic acid were utilised in double-Mannich reactions with bis(aminol)ethers to develop an asymmetric synthesis of azabicyclo[3.3.1]nonanes. An improved method for the double-Mannich reaction of β-ketoesters and bis(aminol)ethers using sub-stoichiometric quantities of a Lewis acid was developed. Additionally, a sequential, double-Mannich approach was investigated incorporating chiral auxiliaries into N , O -acetals. The use of oxazolidinone auxiliaries afforded the best yields and diastereoselectivities enabling separation of the resulting diastereomers of the azabicyclo[3.3.1]nonanes. [ABSTRACT FROM AUTHOR]

A range of structurally diverse chiral spiro[imidazolidine-2-thione-4,3′-oxindole] compounds could be obtained via a domino Mannich-cyclization reaction of 3-isothiocyanato oxindoles and imines with commercial quinine as catalyst under mild conditions. The protocol is significantly characterized by simple process, easily available catalyst, high reactivity, low catalyst loading (1 mol %), and good to excellent diastereo- and enantioselectivity (up to>99:1 dr and 97% ee). A plausible dual activation working model was tentatively proposed to account for the stereochemistry of the domino Mannich-cyclization process. [ABSTRACT FROM AUTHOR]

In the current study, new polysubstituted nitropyridimines were efficiently synthesized via double Mannich cyclizations of diaryl substituted β-nitroenamines with formaldehyde and aniline derivatives under microwave irradiation for 30–40 min. Furthermore, an antioxidant study showed that some of the nitropyridimines have moderate to low scavenging activity against DPPH radical. Also, in a preliminary antibacterial activity test of selected products, only one product exhibited moderate antibacterial effect against S.Epidermidis bacteria. To create your abstract, type over the instructions in the template box below.Fonts or abstract dimensions should not be changed or altered. [Display omitted] [ABSTRACT FROM AUTHOR]

The conjugate addition nitro-Mannich reactions of ethyl-β-nitroacrylate ( 1 ) and β-nitrostyrene ( 2 ) with electron rich aromatic nucleophiles, stabilized carbanions, alcohols, amines, thiols, and diphenyl phosphine oxide were investigated. The one pot conjugate addition nitro-Mannich reaction was unsuccessful except for the addition of alkoxides to 2 in alcohol as solvent. Isolation of the conjugate addition products followed by deprotonation with n BuLi and treatment with a simple imine in the presence of TFA led to β-nitroamine derived products. Products derived from 1 spontaneously cyclised in only a few examples and on the whole led to inherently unstable products. Products derived from 2 were isolated as their trifluoroacetamides, gave good yields of single diastereoisomers for aromatic and alkoxide nucleophiles and the structures were verified by single crystal X-ray crystallography. Products derived from amine nucleophiles were isolated in low yields while sulfur nucleophiles gave poor diastereoselectivities. [ABSTRACT FROM AUTHOR]

A multicomponent, Mannich-type assembly process commencing with commercially available bromobenzaldehydes was sequenced with [3+2] dipolar cycloaddition reactions involving nitrones and azomethine ylides to generate collections of fused, bicyclic scaffolds based on the 2-arylpiperidine subunit. Use of the 4-pentenoyl group, which served both as an activator in the Mannich-type reaction and a readily-cleaved amine protecting group, allowed sub-libraries to be prepared through piperidine N-functionalization and cross-coupling of the aryl bromide. A number of these derivatives displayed biological activities that had not previously been associated with this substructure. Methods were also developed that allowed rapid conversion of these scaffolds to novel, polycyclic dihydroquinazolin-2-ones, 2-imino-1,3-benzothiazinanes, dihydroisoquinolin-3-ones, and bridged tetrahydroquinolines. [ABSTRACT FROM AUTHOR]

Abstract: A task-specific ionic liquid with a Bronsted acid (1-(3-sulfopropyl)-3-methylimidazolium hydrogen sulfate, namely MSI) bearing an anionic heteropolyacid derivative ([PW12O40]3−, namely PW) were used as an efficient catalyst for the three-component Mannich and Hantzsch reactions. Using (MSI) 3 PW as the catalyst supported in imidazolium-based ionic liquids allowed these multicomponent reactions to take place in good to excellent yields. The Mannich reaction, performed at room temperature, was also evaluated by means of electrospray (tandem) mass spectrometry—ESI-MS(/MS). ESI-MS data pointed to the origin of the ionic liquid effect, i.e., formation of ion pairs with the charged reaction intermediates and furthers association into larger supramolecular aggregates. DFT calculations revealed the strength of the supramolecular interactions between the charged species detected by ESI-MS and the spontaneity association of these ion pairs affording larger supramolecular aggregates. [Copyright &y& Elsevier]

Abstract: Several 6-substituted-8-nitrothiazolo[3,2-c]pyrimidine derivatives have been obtained very efficiently by a multicomponent cyclisation of 2-(nitromethylene)thiazolidine, formaldehyde and various aliphatic or aromatic amines in water, using both microwave irradiation and conventional heating. Reaction yields were considerably higher and the reaction times very much reduced using microwave heating when compared to conventional heating, resulting in the definition of a rapid and efficient synthetic protocol. [Copyright &y& Elsevier]

Abstract: The formyl group at the 3-position of methyl pyropheophorbide-d, one of chlorophyll-a derivatives, was efficiently transformed to the 32-cis-unsubstituted/methyl- or 32-cis-phenyl-32-trans-nitro-vinyl groups by Henry (nitro-aldol) or nitro-Mannich (aza-Henry) reactions with nitromethane/ethane or nitrophenylmethane, respectively. The introduction of a nitro group at the terminal of the 3-ethenyl moieties directly connected with the chlorin π-system red-shifted and broadened their Qy electronic absorption and fluorescence emission bands in a solution. The fluorescence intensities were largely suppressed by the substitution with the nitro group. [Copyright &y& Elsevier]

Abstract: The generality of (S)-2-chlorotetrafluoroethanesulfinamide (CTFSA) induced asymmetric vinylogous Mannich (AVM) addition reaction has been investigated. The reaction of aldimines derived from (S)-CTFSA with 2-(tert-butyldimethylsilyloxy) furan (TBSOF) took place regioselectively at the γ-site at room temperature in DMSO under air atmosphere to give the desired addition products in syn-configuration with high diastereoselectivities (up to 98:2 dr). However, anti-configuration product as major isomer was obtained in the presence of tetra-butyl ammonium fluoride (TBAF) at −78 °C. Facile removal of the auxiliary group without epimerization demonstrated their synthetic potential for piperidone derivatives. [Copyright &y& Elsevier]

Abstract: A new family of C 2-axially chiral monophosphines (Ar-NNPs) from Ar-BINMOLs was developed for silver-catalyzed asymmetric vinylogous Mannich reaction of (furan-2-yloxy)trimethylsilane with aromatic aldimines. It was found that the enantioselective vinylogous Mannich-type reactions of trimethylsiloxyfuran with aldimines are catalyzed efficiently by silver(I) complexes of the Ar-BINMOL-derived chiral monophosphine. This procedure displays wide aldimine versatility, excellent yields (up to 99% isolated yields), moderate to good enantioselectivity (up to 78%ee) and exceptional diastereoselectivity (>99:1 dr) in most cases examined. The molecular structure of silver–monophosphine complex was confirmed by X-ray analysis and revealed that the benzyl group on chiral monophosphine provided dual function with weak silver–π/π–π stacking and steric repulsion to favour the diastereoselective Re-nucleophilic addition of siloxyfuran to imine. [Copyright &y& Elsevier]

Abstract: Oxadisilole-fused-3,4-dihydro-2H-naphtho[2,1-e]-1,3-oxazines and 3,4-dihydro-2H-anthra[2,1-e]-1,3-oxazines were synthesized through an eco-friendly Mannich type condensation–cyclization reaction of oxadisilole-fused-1-naphthalenol or 1-anthracenol with formaldehyde and primary amines at ambient temperature in high to excellent yields. The photophysical, electrochemical, and thermal properties of these 3,4-dihydro-2H-anthra[2,1-e]-1,3-oxazine derivatives were also studied. [Copyright &y& Elsevier]

Abstract: An efficient, convergent, and highly stereoselective formal synthesis of amphidinin B (1) is reported herein. In Amphidinin B both C10–C21 (4) and C1–C9 (5) fragments were derived from geraniol 6 and mono-PMB ether of 1,4-butane diol 7 in 19 and 9 steps, respectively. The key steps involved in this synthesis are Sharpless asymmetric epoxidation, Evans aldol, Julia olefination, oxa-Michael, Keck allylation, Mannich reaction, Evans asymmetric alkylation, and Yamaguchi esterification. [Copyright &y& Elsevier]

Abstract: A series of novel calix[4]arene-based Mannich (5 and 6) and Schiff base (9–11) receptors have been synthesized and characterized by various analytical techniques. Competitive two-phase extraction experiments of these novel calix[4]arene amine- and imine-containing derivatives revealed a strong affinity for dichromate anions . The protonated alkylinium form of 5, 6 and 9–11 proved to be effective extractants for transferring the dichromate anions from an aqueous into an organic phase. Moreover, the extraction of dichromate anions by 5 and 9 in the presence of competitive anions such as F−, Cl−, Br−, , , and showed that 5 and 9 could be selective anion receptors for dichromate anions in the presence of those anions. [Copyright &y& Elsevier]

Abstract: A zinc carbenoid-initiated chain extension reaction provides access to an organometallic intermediate, which can be used to capture activated imines. Deprotection of the nitrogen and reduction provides access to racemic derivatives of β-proline. The relative stereochemistry of the β-proline can be controlled through use of different activating groups on the imine nitrogen. [Copyright &y& Elsevier]

Abstract: Catalytic Mannich-type reactions of 9-fluorenylidene-protected α-aminoacetonitrile with imines were investigated. The desired reactions proceeded smoothly to afford the Mannich-type adducts in high yields with high diastereoselectivities in the presence of a catalytic amount of 1,1,3,3-tetramethylguanidine (TMG). A chiral guanidine catalyzed the reaction with good enantioselectivity. [Copyright &y& Elsevier]