p‐TSA‐Based DESs as “Active Green Solvents” for Microwave Enhanced Cyclization of 2‐Alkynyl‐(hetero)‐arylcarboxylates: an Alternative Access to 6‐Substituted 3,4‐Fused 2‐Pyranones

Abstract

In this paper, we describe the use of p‐TSA based Deep Eutectic Solvents (DESs) as alternative environmental‐friendly “active” solvents for the microwave‐mediated synthesis of 6‐substituted 3,4‐fused 2‐pyranones, and in particular isocoumarins, starting from 2‐alkynyl‐(hetero)arylcarboxylates. When the alkyne terminus bears a neutral or an electron‐donating group (EDG), the reactions are fast, clean and highly regioselective, to give the 6‐endo‐dig cyclization products in good to excellent yields. For substrates bearing an electron‐withdrawing group (EWG) on the alkyne end, the regioselectivity can be tuned by adding a small amount of silver(I) triflate as co‐catalyst. DES was demonstrated to be reusable without loss of efficiency in terms of reaction yields. Based on experimental evidence and previous findings, two competitive mechanisms working simultaneously are proposed to explain the outcomes and the regioselectivity issues.

A New Alkylation of Aryl Alcohols by Boron Trifluoride Etherate

“…Methyl o-iodobenzoate 17 [32]; colorless liquid, 0.9441g (89% yield. 1 H NMR (400 MHz, Chloroform) δ 7.95 (d, J = 7.83 Hz, 1H), 7.76 (d, J = 7.44 Hz, 1H), 7.36 (t, J = 7.63 Hz, 1H), 3.90–7.11 (t, J = 7.44 Hz, 1H).…”

Silver‐catalysed A3‐coupling reactions in phenylacetic acid/alkylamineN‐oxide eutectic mixture under dielectric heating: An alternative approach to propargylamines

“…[ 34 ] In this work, the authors tested the reactivity of several different alkyl and (hetero)aryl aldehydes, whereas the assortment of alkynes and amines was very limited. Based on our recent experience in MW‐promoted/silver‐catalysed multicomponent synthesis of propargylamines [ 35 ] and the use of acidic DESs as alternative media for the MW‐enhanced synthesis of 3,4‐fused 2‐pyranones, [ 36 ] we were intrigued to explore the scope and limitation of Ag‐catalysed/MW‐promoted A 3 ‐coupling in our acidic DESs (Figure 1). Based on our experience in the use of complexes of silver with pyridine‐containing ligands [PcL] as catalysts for transformations involving alkynes, [ 37 ] we planned to test the activity of one of the more active Ag[PcL] complex (Figure 1).…”

A Ag2CO3/TFA-catalyzed intramolecular annulation approach to imidazo[1,2-c][1,3]oxazin-5-one derivatives

“…14 Synthetically, the asymmetrical activation of the Csp–Csp bond of 2-alkynylbenzoates to trigger intramolecular cyclization has been accomplished by three main methods. The first one was performed using a catalytic amount of a Brønsted acid such as TFA, 13,15,16 PTSA 17–19 or TfOH 12,20,21 leading to the formation of 5- or 6-membered lactones (Fig. 1a).…”