Tandem One-Pot Synthesis of Polysubstituted Pyridines Using the Blaise Reaction Intermediate and 1,3-Enynes

Recent advances in the tandem annulation of 1,3-enynes to functionalized pyridine and pyrrole derivatives

Great progress has been made in the tandem annulation of enynes in the past few years. This review only presents the corresponding reactions of 1,3-enyne structural motifs to provide the functionalized pyridine and pyrrole derivatives. The functionalization reactions cover iodination, bromination, trifluoromethylation, azidation, carbonylation, arylation, alkylation, selenylation, sulfenylation, amidation, esterification, and hydroxylation. We also briefly introduce the applications of the products and the reaction mechanisms for the synthesis of corresponding N-heterocycles.

An Isoxazole Strategy for the Synthesis of Fully Substituted Nicotinates

A four-step quasi one-pot procedure for the preparation of fully substituted nicotinates from ketone enamines and 4-methylideneisoxazol-5-ones has been developed. The reaction sequence involves (1) reaction of 4-methylideneisoxazol-5-ones with ketone enamines with the formation of isoxazole-5-ols, (2) their O-methylation with diazomethane, (3) hydrogenative cleavage of the O-N bond in 5-methoxyisoxazoles under action of Mo(CO)₆/H₂O and simultaneous isomerization and condensation of the formed enamines, with the formation of dihydropyridines, and (4) aromatization of the latter.

Cobalt(ii)-catalyzed hydroarylation of 1,3-diynes and internal alkynes with picolinamides promoted by alcohol

The Co(ii)-catalyzed selective C-H alkenylation of picolinamides with 1,3-diynes has been developed. This protocol can be applied to a variety of 1,3-diynes. In addition, both symmetrical and unsymmetrical internal alkynes were well tolerated, affording the corresponding alkenyl arenes. Moreover, control experiments indicated that C-H bond cleavage may be involved in the rate-determining step. Furthermore, a deuterium incorporation product was achieved when deuterated alcohol was employed as the solvent, which suggested that alcohol was essential for the final protonolysis.

A Review on Onychine and its Analogs: Synthesis and Biological Activity

BACKGROUND

Onychine is a 4-azafluorenone alkaloid isolated from the Annonaceae family, in low concentrations. Onychine and its analogs exhibit a wide range of pharmacological activities such as antifungal, antibacterial, anticancer, and antimalarial. Because of the high bioactivity of some 4-azafluorenone derivatives, several synthetic methods have been developed for their procurement.

OBJECTIVE

Considering the importance of these alkaloids, we aim to present the main synthetic approaches to onychines and its derivatives and the biological activity of some 4-azafluorenones.

METHODS

The most prominent methodologies for the synthesis of onychines were reviewed.

RESULTS

In this work, we cover many synthetic approaches for the synthesis of onychine and 4-azafluorenone derivatives including intramolecular cyclizations, multicomponent reactions, microwave-assisted multicomponent reactions, Diels-alder reactions, among others. Moreover, we also review the biological activity of 4-azafluorenones.

CONCLUSION

4-azafluorenones have risen as prominent structures in medicinal chemistry; however, most of the time, access to new derivatives involves toxic catalysts, harsh reaction conditions, and long-step procedures. Therefore, the development of new synthetic routes with more operational simplicity, simple purification procedure, good yields, and low environmental impact, is desirable.

Synthesis of (E)-1,4-disilsesquioxylsubstituted but-1-en-3-ynes via platinum-catalyzed dimerization of ethynylsiloxysilsesquioxanes

A new platinum complex bearing bulky N-heterocyclic carbene ligand of the general formula [Pt(IPr*Ph)(dvtms)] (where IPr*Ph = 1,3-bis{2,4,6-tris(diphenylmethyl)phenyl}imidazol-2-ylidene, dvtms = divinyltetramethyldisiloxane) exhibits a high catalytic activity towards E-selective dimerization of ethynyl substituted siloxysilsesquioxanes. This process leads to a novel class of functionalized silsesquioxane derivatives, resembling their dumbbell-shaped silsesquioxane analogues.

A new strategy for the synthesis of pyridines from N-propargylic β-enaminothiones

A new robust method for the synthesis of 2,4,5-trisubstituted pyridines with high efficiency and broad functional group tolerance is described.

Tailor-made synthesis of fully alkylated/arylated nicotinates by FeCl3-mediated condensation of enamino esters with enones

A synthetic method for fully alkylated/arylated nicotinates was achieved by FeCl₃-mediated condensation of enamino esters and enones.

Facile synthesis of heavily-substituted alkynylpyridines via a Sonogashira approach

A robust synthesis of highly-substituted alkynylpyridines via a Sonogashira approach is described, providing a library of functionalized pyridines for biological studies.

Three-component, one-pot synthesis of benzo[6,7]cyclohepta[1,2-b]pyridine derivatives under catalyst free conditions and evaluation of their anti-inflammatory activity

An efficient three-component protocol is described for the synthesis of benzo[6,7]cyclohepta[1,2-b]pyridine derivatives using β-chloroacroleins, 1,3-dicarbonyls and ammonium acetate under catalyst free conditions by using ethanol as reaction media. The mild reaction conditions, operational simplicity and high yields are the advantages of this protocol and the broad scope of this one-pot reaction makes this procedure promising for practical usages. All the final compounds were screened for anti-inflammatory activity. Among the compounds tested, the compounds 5a, 5b, 5c, 5d, 5f, and 5k exhibited significant inhibition of IL-1β and MCP-1 secretion as a measure of anti-inflammatory activity.

Advances in tandem reactions with organozinc reagents

A review of recent advances in tandem reactions with organozinc reagents that highlight their utility in organic synthesis.

Synthesis of new chiral lactam-fused pyridine derivatives

An acid promoted cyclisation of benzylidene-modified tetramic acid and various enamines followed by MnO₂ oxidation afforded the corresponding C₂-symmetric and unsymmetric lactam-fused pyridines in enantiomerically pure forms.

Synthesis of benzofuro[2,3-c]pyridines via a one-pot three-component reaction

A convenient one-pot synthesis of polysubstituted benzofuro[2,3-c]pyridines by three-component is developed. It provides a flexible and rapid synthetic route for the construction of benzofuro[2,3-c]pyridines under mild and metal-free reaction conditions in moderate to good yields (up to 83%).

Synthesis of fully-substituted pyridines and dihydropyridines in a highly chemoselective manner utilizing a multicomponent reaction (MCR) strategy

An efficient protocol has been developed for the synthesis of pyridines and 1,4-dihydropyridines based on chemoselective multicomponent reactions.

Synthesis of naphthalene amino esters and arylnaphthalene lactone lignans through tandem reactions of 2-alkynylbenzonitriles

A novel and efficient synthesis of naphthalene amino esters and arylnaphthalene lactone lignans via the tandem reaction of 2-alkynylbenzonitriles is presented.

Pyridine synthesis by reactions of allyl amines and alkynes proceeding through a Cu(OAc)2 oxidation and Rh(III)-catalyzed N-annulation sequence

A new methodology has been developed for the synthesis of pyridines from allyl amines and alkynes, which involves sequential Cu(II)-promoted dehydrogenation of the allylamine and Rh(III)-catalyzed N-annulation of the resulting α,β-unsaturated imine and alkyne.

Rhenium-catalyzed regioselective synthesis of multisubstituted pyridines from β-enamino ketones and alkynes via C-C bond cleavage

A new method is described for the regioselective synthesis of multisubstituted pyridine derivatives. Treatment of N-acetyl β-enamino ketones with alkynes in the presence of the rhenium catalyst, Re(2)(CO)(10), gives multisubstituted pyridines regioselectively. In this reaction, the N-acetyl moieties are important for the selective formation of the multisubstituted pyridines. This reaction proceeds via insertion of alkynes into a carbon-carbon single bond of β-enamino ketones, intramolecular nucleophilic cyclization, and elimination of acetic acid.

tert-Butyl 6-amino-5-cyano-2-(2-methoxyethyl)nicotinate

The title compound, C₁₄H₁₉N₃O₃, was synthesized by the reaction of 3-meth­oxy­propionitrile, tert-butyl bromo­acetate and eth­oxy­methyl­enemalononitrile. In the crystal, N—H⋯O hydrogen bonds link the mol­ecules into chains propagating along the b axis.