Convenient syntheses of unsymmetrical imidazolidines

Stereospecific Single-Pot Route to Chiral Imidazolidines from Aziridines Using a 2D Cu Metal-Organic Framework

The role of coordinatively unsaturated sites (CUS) in metal-organic framework (MOF)-catalyzed organic transformation is vital; however, the design and generation of such sites are challenging. We, therefore, report the synthesis of a novel two-dimensional (2D) MOF, [Cu(BTC)(Mim)]_n (Cu-SKU-3), with pre-existing unsaturated Lewis acid sites. The presence of these active CUS facilitates a ready-to-use attribute in Cu-SKU-3, thereby subsiding the lengthy activation processes associated with MOF-based catalysis. The material has been completely characterized using single crystal X-ray diffraction (SCXRD), powder XRD (PXRD), thermogravimetric analysis (TGA), carbon, hydrogen, and nitrogen (CHN), Fourier-transform infrared (FTIR), and Brunauer-Emmett-Teller (BET) surface area analyses. We directly utilize Cu-SKU-3 for the synthesis of biologically valued chiral imidazolidine motifs in a one-pot fashion starting from aziridines. The chiral imidazolidines are synthesized in good yield (up to 89%) and with high optical purity (ee > 98-99%). Mechanistically, the transformation proceeds in a tandem fashion through stereospecific ring-opening of aziridines followed by the intramolecular cyclization (via sp³ C-H functionalization) reaction forming chiral imidazolidines. The material has an excellent heterogeneous attribute and can be reused several times for one-pot catalytic cycles.

Organocatalytic Asymmetric [3 + 2]-Annulations of γ-Sulfonamido/γ-Hydroxy-α,β-Unsaturated Ketones with Cyclic N-Sulfimines: Synthesis of Chiral Polyheterotricyclic Imidazolidines and Oxazolidines

The first organocatalytic asymmetric [3 + 2]-annulation of γ-sulfonamido-α,β-unsaturated ketones with cyclic N-sulfimines has been developed, and enantioenriched functionalized polyheterotricyclic imidazolidines were obtained in good yields and with excellent enantioselectivities. This approach was also extended to the asymmetric [3 + 2]-annulation of γ-hydroxy-α,β-unsaturated ketones, affording enantioenriched polyheterotricyclic oxazolidines. In addition, base-catalyzed [3 + 2]-annulations of γ-sulfonamido/γ-hydroxy-α,β-unsaturated ketones with cyclic N-sulfimines were re-investigated under mild reaction conditions for the synthesis of racemic polyheterotricyclic imidazolidines and oxazolidines with excellent diastereoselectivities.

Enantioselective [3+2] Cycloaddition of Donor-Acceptor Aziridines and Imines to Construct 2,5-trans-Imidazolidines

An enantioselective [3+2] cycloaddition of donor-acceptor aziridines with N-aryl protected imines was developed with a Ni(ClO₄ )₂  ⋅ 6H₂ O/N,N'-dioxide catalyst system, providing a broad range of chiral trans-substituted imidazolidine compounds with good yields and excellent enantioselectivities (up to 99 % yield, up to 98 % ee). Control experiments indicated that the products could offer excellent diastereoselectivities with the control of chiral Ni(II)-N,N'-dioxide complex and the interaction of the substrates. The possible catalytic process was proposed to rationalize the stereocontrol.

CsPbBr3 perovskite quantum dots as a visible light photocatalyst for cyclisation of diamines and amino alcohols: an efficient approach to synthesize imidazolidines, fused-imidazolidines and oxazolidines

We report the synthesis of highly stable CsPbBr3QD based photocatalysts using dibromoisocyanuric acid (DBI) as a benign non-toxic bromide precursor.

Stereoselective Syntheses of Highly Functionalized Imidazolidines and Oxazolidines via Ring-Opening Cyclization of Activated Aziridines and Epoxides with Amines and Aldehydes

A mild one-pot stereospecific synthetic route to highly functionalized imidazolidines and oxazolidines via S_N2-type ring-opening of the corresponding activated aziridines and epoxides with amines followed by p-toluenesulfonic acid (PTSA)-catalyzed intramolecular cyclization with aldehydes has been developed. The methodology tolerates a variety of functional groups and furnishes the desired products in high yields (up to 92%) with excellent stereoselectivities (de, ee > 99%). Interestingly, imidazolidines were formed as the cis-isomers, whereas oxazolidines were produced as trans-isomers exclusively.

Diversity-Oriented Approach to N-Heterocyclic Compounds from α-Phenyl-β-enamino Ester via a Mitsunobu-Michael Reaction Sequence

Herein we delineate a novel route for the diastereoselective construction of diversely substituted N-heterocyclic ring systems as valuable scaffolds for natural products and pharmaceuticals, starting from an easily accessible prochiral α-phenyl-β-enamino ester. The reaction sequence relies on the unexplored reactivity of α-phenyl-β-enamino ester as a nucleophilic partner in the Mitsunobu reaction to forge the N-tethered alkene-alcohol/thiol/amine intermediate, which was subjected to an intramolecular hetero-Michael addition reaction under mild conditions to furnish the respective N-heterocyclic compounds embedded with an exocyclic chiral center in high yields and excellent diastereoselectivities. The methodology is amenable for a broad range of substrates based on a metal-free approach.

Formation and conversion of six temperature-dependent fluorescent ZnII-complexes containing two in situ formed N-rich heterocyclic ligands

Formation and conversion of six temperature-dependent fluorescent Zn^II-complexes containing two solvothermal in situ formed N-rich heterocyclic ligands from simply N₃ set Schiff base were systematically studied for the first time.

1,2,3-Triazoles

Rapid progress in the synthetic application of benzotriazole derivatives in the last 20 years has resulted in over 1000 scientific papers on the subject. This fact is reflected in Section 5.01.7, which involves almost a half of the volume of this chapter. The section is arranged according to hybridization of the C-α atom and atomic numbers of the atoms in positions β and γ to allow an easy access to the material of interest. Recent discovery of copper catalysis in [3+2] cycloadditions of azides to acetylenes, the so-called ‘click chemistry’, which boosted application of the 1,2,3-triazole derivatives, especially in medicinal chemistry, is presented in Section 5.01.9. From the point of view of practical applications, Section 5.01.11 is organized according to the number, position, and combination of the substituents at the aromatic rings. Another novel feature that has no precedence in the previous editions of Comprehensive Heterocyclic Chemistry is an addition of triazole and benzotriazole complexes with various transitions metals to Section 5.01.4.

Synthesis, characterization and in vitro biological studies of novel cyano derivatives of N-alkyl and N-aryl piperazine

Cyano derivatives of N-alkyl and N-aryl piperazine have been synthesized and screened for antibacterial and antifungal activities. All the synthesized compounds showed the antibacterial activity against pathogenic strains of Staphylococcus aureus (MTCCB 737), Pseudomonas aeruginosa (MTCCB 741), Streptomyces epidermidis (MTCCB 1824) and Escherichia coli (MTCCB 1652) and antifungal activity against pathogenic strains of Aspergillus fumigatus (ITCC 4517), Aspergillus flavus (ITCC 5192) and Aspergillus niger (ITCC 5405). All compounds showed mild to moderate antimicrobial activity. However, compounds 3c, 4a and 6 showed potent antibacterial activity against pathogenic strains used in the study. Compounds 3a, 3b, 4b, and 4d showed mild to moderate antifungal activity against Aspergillus pathogenic strains. The compounds reported in this study were assessed for there cytotoxicity using MTT colorimetric assay on Hela cells. All the compounds showed cell viability more than the control drug gentamicin, with compound 2 having highest i.e. 95% cell viability.

Synthesis of new unsymmetrical 4,5-dihydroxy-2-imidazolidinones. Dynamic NMR spectroscopic study of the prototropic tautomerism in 1-(2-benzimidazolyl)-3-phenyl-4,5-dihydroxy-2-imidazolidinone

The acid-catalyzed cyclocondensation in refluxing acetonitrile of aqueous glyoxal with N-heteroaryl-N'-phenylureas 4a-f (heteroaryl = 2-thiazolyl, 2-pyrimidinyl,2-pyrazinyl, 2-pyridinyl, 3-pyridinyl and 2-benzimidazolyl) led to the formation of the corresponding 1-heteroaryl-3-phenyl-4,5-dihydroxy-2-imidazolidinones 5a-f. All the products were characterized by elemental and spectroscopic analyses. The free-energy barrier (Delta G not equal) for prototropic tautomerism in 1-(2-benzimidazolyl)-3-phenyl-4,5-dihydroxy-2-imidazolidinone (5f) was determined by dynamic NMR studies to be 81 +/- 2 KJ mol(-1).

Novel reaction of N,N'-bisarylmethanediamines with formaldehyde. Synthesis of some new 1,3,5-triaryl-1,3,5-hexahydrotriazines

The acid-catalyzed cyclocondensation of N,N'-bisaryl (aryl = 2-pyrimidinyl, 2-pyrazinyl and 4-nitrophenyl) methanediamines 5a-c with aqueous formaldehyde in refluxing acetonitrile leads to the formation of the corresponding 1,3,5-triaryl-1,3,5-hexa-hydrotriazines 6a-c. The stoichiometric reactions of 2-aminopyrimidine and 2-amino-pyrazine with aqueous formaldehyde in acetonitrile under reflux conditions also afforded 6a and 6b, respectively. Treatment of 2-aminopyrimidine with aqueous formaldehyde in a 3:2 ratio yielded N,N',N"-tris(2-pyrimidinyl)dimethylenetriamine (7a) as a sole product, which upon subsequent reaction with formaldehyde also afforded 6a. The reaction of N,N'-biphenylmethanediamine with formaldehyde was also investigated.

Synthesis and antimicrobial activity of N-alkyl and N-aryl piperazine derivatives

A series of substituted piperazine derivatives have been synthesized and tested for antimicrobial activity. The antibacterial activity was tested against Staphylococcus aureus (MTCCB 737), Pseudomonas aeruginosa (MTCCB 741), Streptomyces epidermidis (MTCCB 1824) and Escherichia coli (MTCCB 1652), and antifungal activity against Aspergillus fumigatus, Aspergillus flavus and Aspergillus niger. All synthesized compounds showed significant activity against bacterial strains but were found to be less active against tested fungi. In vitro toxicity tests demonstrated that compounds 4d and 6a showed very less toxicity against human erythrocytes.

Selective product amplification of thymine photodimer by recognition-directed supramolecular assistance

Two symmetric ditopic supramolecular templates (1 and 2) each presenting two hydrogen bonding recognition subunits were synthesized. Each such subunit comprises the same donor and acceptor pattern, capable of binding a substrate molecule with complementary hydrogen bonding groups to form a supramolecular complex. Substrate molecules, such as thymine or uracil derivatives, yield 2 : 1 complexes with the acceptors involving two hydrogen bonds to each subunit with ideal orientation for subsequent [2 + 2] dimerization upon photoirradiation. Selective syn photoproduct formation and concomitant suppression of the trans isomer are favored by orientation of the two guest nucleobases within the template cleft. Complementary donor and acceptor hydrogen bonding induced positioning of the two substrates and steric hindrance within the template clefts are responsible for the selective product formation.

Preparation of Tertiary Alkyl Carbinamines, Propargylamines, and α-Heteroarylamines by Ketone-Based Aminoalkylation

Ketones 6a-i were converted into their benzotriazolylamine adducts 8a-i either directly from the corresponding ketone 6a or via enamines 7b-i. Adducts 8a-i on treatment with Grignard reagents, lithium phenylacetylide, or heteroaryllithiums gave tertiary alkyl carbinamines 9a-h (47-61%), propargylamines 10a-i (30-98%), and alpha-heteroarylamines 11a-k (44-85%), respectively.

Novel Synthesis of 1,2,3,4-Tetrahydropyrazino[1,2-a]indoles

Condensation of 2-(3-methyl-1H-indol-1-yl)ethylamine (7) with benzotriazole and formaldehyde gave 2-(1H-1,2,3-benzotriazol-1-ylmethyl)-10-methyl-1,2,3,4-tetrahydropyrazino[1,2-a]indole (8) in 96% yield. Nucleophilic substitutions of the benzotriazolyl group in 8 with NaBH(4), NaCN, triethyl phosphite, allylsilanes, silyl enol ether and Grignard reagents afforded novel 10-methyl-1,2,3,4-tetrahydropyrazino[1,2-a]indoles 9a-i in 78-95% yields.

Novel syntheses of enantiopure hexahydroimidazo[1,5-b]isoquinolines and tetrahydroimidazo[1,5-b]isoquinolin-1(5H)-ones via iminium cation cyclizations

Condensations of chiral diamines 11a-c with benzotriazole and formaldehyde gave benzotriazolyl intermediates 12a-c; similar condensations of alpha-amino-amides 10a-c with benzotriazole and paraformaldehyde gave 14a-c. Subsequent treatment of 12a-c and 14a-c with AlCl(3) led to enantiopure tricyclic 1,2,3,5,10,10a-hexahydroimidazo[1,5-b]isoquinolines 1a-c and 2,3,10,10a-tetrahydroimidazo[1,5-b]isoquinolin-1(5H)-ones 15a-c, respectively, via Lewis acid promoted iminium cation cyclizations.