ZnCl2-Promoted One-Pot Three-Component Synthesis of Multisubstituted Thiazolo[4,5-b]pyridines and Thieno[2,3-b:4,5-b′]dipyridines

Vilsmeier-Haack Cyclisation as a Facile Synthetic Route to Thieno [2,3- b] Quinolines (Part I)

Abstract:

Quinoline ring system is extensively dispensed in natural products, especially in alkaloids. Moreover, thieno[2,3-b]quinolines have vast biological activities, including urea transporter inhibition, anti-microbial, antitumor, antioxidant, anti-inflammatory, and antiproliferative EGFR tyrosine kinase inhibition. Vilsmeier-Haack is considered the most facile and promising set of synthetic routes, leading to 2-chloro-3-formylquinolines through Vilsmeier-Haack cyclisation of N- arylacetamides, which are subsequently used as key intermediates for the synthesis of thieno[2,3-b]quinolones (Tqs). Many varieties of thieno[2,3-b]quinolines (Tqs) ring systems, specifically concerning medicinal chemistry, have been developed over the past decade. In light of these facts, this review presents a systematic and comprehensive survey of the method of preparation and the chemical reactivity of thieno[2,3-b]quinolines through the Vilsmeier-Haack reaction. In this study, the methods of preparation and the chemical reactivity of (Tqs) by using the Vilsmeier-Haack reaction are discussed. Since the beginning of the 21st century, they have been advancing towards synthesizing substituted Tqs. It can be concluded that substituted Tqs can be used as building blocks for the synthesis of polyfunctionalized heterocyclic compounds with pharmacological interest.

Domino Synthesis of Thiazolo-Fused Six- and Seven-Membered Nitrogen Heterocycles via Intramolecular Heteroannulation of In-Situ-Generated 2-(Het)aryl-4-amino-5-functionalized Thiazoles

Synthesis of novel 2-(het)aryl-substituted thiazolo-fused six- and seven-membered heterocycles, such as thiazolo[4,5-b]pyridin-5(4H)-ones, thiazolo[4,5-c]isoquinolin-5(4H)-ones, thiazolo[4,5-b]quinolin-9(4H)-ones, 4H-benzo[e]thiazolo[4,5-b]azepine-5,10-diones, have been developed in a single-pot operation via intramolecular heteroannulation of in-situ-generated 2-(het)aryl-4-amino-5-functionalized thiazoles. These 4-amino-5-functionalized thiazoles were readily obtained in a one-pot process by treatment of a range of (het)aryldithioesters with cyanamide in the presence of NaH, followed by in situ S-alkylation-intramolecular condensations of the resulting thioimidate salts with appropriate activated methylene halides. On the other hand, the corresponding 4H-benzo[b]thiazolo[4,5-e][1,4]diazepin-10(9H)-ones were synthesized in a two-step process, requiring prior isolation of 5-carboethoxy-4-(2-nitrophenyl)aminothiazoles and their subsequent reductive cyclization. The activated methylene halides employed in these reactions for the synthesis of various thiazolo-fused heterocycles were methyl bromocrotonate, ethyl 2-(bromomethyl)benzoate, 2-fluorophenacyl bromides, ethyl 2-(2-bromoacetyl)benzoate, and ethyl bromoacetate. Several of these thiazolo-fused heterocycles display yellow green to green fluorescence, and their absorption and emission spectra have also been examined.

Diversity-oriented and diastereoselective synthesis of diverse polycyclic thieno(2,3-b)-quinoline derivatives using a synergistic strategy

A cascade spiroannulation of 2-mercaptoquinoline-3-carbaldehydes with α,α-dicyanoalkenes as well as a cascade spiroannulation of 2-mercaptoquinoline-3-carbaldehydes aldehydes with α-bromocarbonyl compounds was investigated based on a synergistic strategy, providing a series of diverse spiro-fused heterocyclic compounds containing more different functional groups. The features of this strategy directed towards molecular complexity and diversity include step economy, mild conditions, and high bond-forming efficiency, but important polycyclic heterocyclic products, which could be transformed into potential biologically interesting heterocyclic structures.

Thiophene Syntheses by Ring Forming Multicomponent Reactions

Thiophenes occur as important building blocks in natural products, pharmaceutical active compounds, and in materials for electronic and opto-electronic devices. Therefore, there is a considerable demand for efficient synthetic strategies for producing these compounds. This review focuses on ring-forming multicomponent reactions for synthesizing thiophenes and their derivatives.

Synthesis of N-aryl 2-quinolinones via intramolecular C(sp2)–H amidation of Knoevenagel products

An efficient synthesis of N-aryl 2-quinolinones via K₂S₂O₈-mediated intramolecular C(sp²)–H amidation of Knoevenagel products was developed.

Crystal structure of 2-(2-methyl-phen-yl)-1,3-thia-zolo[4,5-b]pyridine

In the title mol-ecule, C13H10N2S, the dihedral angle between the planes through the non-H atoms of the methylbenzene and thi-azo-lopyridine groups is 36.61 (5)°. In the crystal, the thi-azo-lopyridine groups of inversion-related mol-ecules overlap, with a minimum ring-centroid separation of 3.6721 (9) Å. Furthermore, the methylbenzene groups from neighbouring mol-ecules inter-act edge-to-face at an angle of 71.66 (5)°. In addition, weak C-H⋯ N hydrogen bonds form chains exending along [100].

Crystal structure of 2-(1-methyl-eth-yl)-1,3-thia-zolo[4,5-b]pyridine

In the title mol-ecule, C9H10N2S, one of the methyl groups is almost co-planar with the thia-zolo-pyridine rings with a deviation of 0.311 (3) Å from the least-squares plane of the thia-zolo-pyridine group. In the crystal, weak C-H⋯N hydrogen-bonding inter-actions lead to the formation of chains along [011].

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.