Synthesis of Fused Pyridines via Microwave-Assisted [3+3] Cyclization

Abstract

A new microwave-assisted p-TsOH-promoted [3＋3] cyclization was developed. By using the characteristics of enaminones or enamino lactones as 1,3-dinucleaphilic reagents and propargyl alcohols as 1,3-electrophilic reagents, p-TsOHpromoted [3＋3] cyclization of these substrates at 70 ℃ was carried out in acetic acid under microwave irradiation, regioselectively affording 2,2-diaryl-substituted tetrahydroquinoline-5(1H)-ones and 2,2-diaryl-substituted dihydrofuro [3,4-b]pyridin-5-ones in good yields. The reaction can be completed within a short period (30 min) by microwave synthetic technology, in which water was the sole by-product. This method features simple and available starting materials, simple operation and wide substrate scope, and provides a green, economic, and efficient synthetic strategy for the construction of fused pyridine skeleton with potential application, which is consistent with the concept of green chemistry.