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

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.