Size mismatch between two tripodal units: A new synthetic strategy for macrotricyclic cryptand
TL;DR: In this article, a matched/mismatched tracer was used to obtain a macrobicyclic/macrotricyclic cryptand in high yield by Schiff base condensation at 5°C in the absence of any templating metal ion.
Abstract: Tripods of matched/mismatched sizes lead to a macrobicyclic/macrotricyclic cryptand in high yield by Schiff base condensation at 5° C in the absence of any templating metal ion.
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TL;DR: A review of reductive aminations using borohydride and borane reducing agents can be found in this article, where the authors focus on those conditions in which the carbonyl component, amine, and reducing reagent react in the same vessel.
Abstract: Reductive amination is an important tool for synthetic organic chemists in the construction of carbon-nitrogen bonds. This reaction, also termed reductive alkylation, involves condensation of an aldehyde or ketone with an amine in the presence of a reducing agent. A wide variety of substrates can be used including aliphatic and aromatic aldehydes and ketones, and even benzophenones. A range of amines from ammonia to aromatic amines, including those with electron-withdrawing substituents, can be employed. For particularly sluggish reactions, such as those involving weakly electrophilic carbonyl groups, poorly nucleophilic amines, or sterically congested reactive centers, additives such as molecular sieves or Lewis acids are often useful.
This chapter focuses on those conditions in which the carbonyl component, amine, and reducing reagent react in the same vessel. This review is restricted to reductive aminations using borohydride and borane reducing agents. This chapter concentrates on reductive amination chemistry mediated by borohydride and other boron-containing reducing agents from 1971, the year when sodium cyanoborohydride was introduced, through the middle of 1999. In addition to reductive aminations of aldehyde and ketone substrates, reactions of related structures including acetals, aminals, ketals, carboxylic acids, nitriles, and dicarbonyls that form a nitrogen-containing ring are reviewed. Intramolecular processes in which the substrate contains both the carbonyl and amine moieties are described. The intramolecular variant is a useful method for preparing cyclic amines. All of the various boron-containing hydride sources in reductive aminations, including labeled metal hydrides, are reviewed. Instances of reductive aminations that failed are described. Applications of this method to a solid support in parallel synthesis in combinatorial chemistry as well as reductive aminations that proceed in tandem with a second reaction such as reductive lactamizations are discussed.
Keywords:
organic reaction(s);
organic synthesis;
reaction(s);
synthesis;
reductive amination;
condensation;
alkylation;
reductive alkylation;
reduction;
amination;
carbonyl;
amine;
reducing agent(s);
borohydride;
borane;
carbon-nitrogen bond(s);
CN bond(s)
136 citations
TL;DR: In this paper, a series of poly(2,6-dimethyl-4-phenyl-1,4-dihydropyridinyl)arenes were synthesized in good yields using a one-pot, acid-catalyzed cyclocondensation reaction of the appropriate poly(aldehydes) with 3-aminobut-2-enenitrile in acetic acid at reflux.
Abstract: A new series of poly(2,6-dimethyl-4-phenyl-1,4-dihydropyridinyl)arenes were synthesized in good yields using a one-pot, acid-catalyzed cyclocondensation reaction of the appropriate poly(aldehydes) with 3-aminobut-2-enenitrile in acetic acid at reflux.
34 citations
TL;DR: Two members of a new class of calix[6]azacryptands, namely, calix:[1 + 1] macrocyclization reaction--reduction sequence and calix,[6]tamb, have been synthesized through an efficient [1 - 1] Macrocyclization Reaction--Reduction sequence.
Abstract: Two members of a new class of calix[6]azacryptands, namely, calix[6]tampo and calix[6]tamb, have been synthesized through an efficient [1 + 1] macrocyclization reaction--reduction sequence. One of them has been obtained in a remarkably high overall yield from the known X(6)H(3)Me(3). In comparison to all the other calix[6]azacryptands, they possess unique conformational properties since they present a rigidified cone conformation with a partial filling of the cavity by the methoxy groups. In contrast to calix[6]tampo, the fully protonated derivative of calix[6]tamb behaves as a remarkable molecular receptor toward polar neutral guests. NMR studies have shown that the intracavity binding process is governed by a conformational flip of the aromatic walls of the calixarene core.
24 citations
TL;DR: In this article, low-temperature synthesis of a number of hetero-polytopic cryptands has been achieved in good yields without employing any templating metal ion, and the cryptands are designed to hold more than one metal ion in its cavity.
Abstract: Low-temperature synthesis of a number of hetero-polytopic cryptands have been achieved in good yields without employing any templating metal ion. The cryptands are designed to hold more than one metal ion in its cavity.
15 citations
References
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TL;DR: The synthesis of a new macrobicyclic cryptand (L) with heteroditopic receptor sites has been achieved in good yields by the [1 + 1] Schiff base condensation of tris(2-aminoethyl)amine (tren) with the tripodal trialdehyde, tris{[2-(oxomethyl)phenyl)oxy]ethyl}amine at 5 degrees C temperature.
Abstract: The synthesis of a new macrobicyclic cryptand (L) with heteroditopic receptor sites has been achieved in good yields by the [1 + 1] Schiff base condensation of tris(2-aminoethyl)amine (tren) with the tripodal trialdehyde, tris{[2-(3-(oxomethyl)phenyl)oxy]ethyl}amine at 5 degrees C temperature. The crystal structure of L (P2(1)/c, a = 10.756 (5) A, b = 27.407(9) A, c = 12.000(2) A, beta = 116.22(3) degrees, Z = 4, R = 0.060, R(w) = 0.058) shows a pseudo-3-fold symmetry axis passing through the two bridgehead nitrogens. This symmetry is maintained in chloroform solution also, as indicated from its (1)H-NMR spectral data. The cryptand readily forms inclusion complexes with the Cu(II) ion at the tren end of the cavity. The tetracoordinated Cu(II) cryptate (1) thus formed with Cu(picrate)(2) exhibits a very small A(II) value (60 x 10(-)(4) cm(-)(1)) in its EPR spectrum and low-energy ligand field bands in its electronic spectrum in MeCN at room temperature. The bound Cu(II) ion readily accepts the anions CN(-), SCN(-), or N(3)(-), forming distorted trigonal bipyramidal complexes (2-4). The crystal structure of [Cu(L)(CN)](picrate) (2) (P2(1)/C, a = 13.099(1) A, b = 11.847(8) A, c = 25.844(7) A, beta = 91.22(1) degrees, Z = 4, R = 0.056, R(w) = 0.054) has been determined. The equatorial coordination is provided by the three secondary amino N atoms of the tren unit in L, while the two axial positions are occupied by the bridgehead N of the tren unit and the C atom of the cyanide group. One of the equatorial Cu-N bond distances is 2.339(6) A, which is longer than normal values. The crystal structure of [Cu(L)(NCS)](picrate) (3) (C2/c, a = 47.889(10) A, b = 10.467(5) A, c = 16.922(2) A, beta = 93.90(2) degrees, Z = 8, R = 0.054, R(w) = 0.055) shows the coordination geometry around the Cu(II) ion to be very similar to that in the case of 2. The electronic spectral and EPR spectral data obtained on 2-4 are characteristic of trigonal bipyramidal Cu(II) complexes. The three meta-substituted benzene rings present in L makes the donor atom somewhat rigid in nature which enforces a distorted geometry around the Cu(II) ion.
67 citations
53 citations
TL;DR: In this paper, the CO-SYSTEMS family of macrotricyclic receptor molecules incorporating [18]-N 2 O 4 units have been synthesized and used as co-receptors, co-catalysts and co-carriers.
Abstract: Macrotricyclic receptor molecules incorporating [18]-N 2 O 4 units have been synthesized. They form mono- and dinuclear ammonium cryptates. Such structures are prototypes of CO-SYSTEMS, whose wide scope as co-receptors, co-catalysts and co-carriers is briefly outlined.
48 citations
36 citations