Recent advances in alkaline earth metal-enabled syntheses of heterocyclic compounds

Abstract

Hetero-cyclic compounds are widely found in natural products, pharmaceuticals and materials, thus drawing the considerable attention from the synthetic community. Commonly, alkaline earth metals are earth abundant and environmentally friendly...

Mg(OtBu)2-catalyzed C–H oxidation of α-azido arylethanones using TBHP as the oxidant and carbonyl oxygen source: facile access to primary α-ketoamides

“…Initially, Mg(O t Bu) 2 possessed both the Lewis acid and the Brønsted base, participating in the coordination of substrate 1a that forms the intermediate A , followed by the release of N 2 gas via dehydroisomerization to afford the imine intermediate B . 7,8 The process is supported by the results of eqn (1), (6) and (7) (Scheme 2). The intermediate B is converted into 5a (without TBHP) or undergoes a deprotonation process with TBHP (the t BuO˙ radical) through single electron transfer (SET) to generate the iminyl carbon-centered radical intermediate C .…”

“…On the basis of the above results and the precedent literature, 3–8 a plausible mechanism was proposed (Scheme 3). Initially, Mg(O t Bu) 2 possessed both the Lewis acid and the Brønsted base, participating in the coordination of substrate 1a that forms the intermediate A , followed by the release of N 2 gas via dehydroisomerization to afford the imine intermediate B .…”

Catalyst-Free Green Synthesis of Phthalazinones at Room Temperature

“…Many important natural products, biologically and pharmacologically active molecules are heterocyclic compounds such as alkaloids, antibiotics, hormones and so on. [1][2][3][4][5][6][7][8] Amongst a range of heterocycles, nitrogen-containing heterocycles are very important core motifs in various biologically active compounds that are frequently found in natural products, pharmaceutical drugs, agrochemicals, and functional materials etc. [9][10][11][12][13] Among the numerous nitrogen-containing heterocycles, phthalazinone is a kind of annulated six-membered N-heterocycles and has diverse biological activities.…”

Chemo- and Stereoselective Synthesis of Substituted Thiazoles from tert-Alcohols Bearing Alkene and Alkyne Groups with Alkaline Earth Catalysts

“…9b On the other hand, calcium salts have been identified as sustainable Lewis acid catalysts for various organic reactions due to their large abundance, biodegradability, non-toxic, less expensive, and moisture-stable features. 10 , 11 Over the past 5 years, our group has been actively engaged in utilizing the Ca(II) catalysts for activating propargyl alcohols toward developing various synthetic methodologies. 11a –c With this experience, we desired to develop a catalytic, synthetic method for thiazole synthesis by treating propargyl alcohols and thioamides in the presence of a Ca(II) catalyst, thereby extending this to the oxazole synthesis.…”

“…Their utility was also extensively studied for the oxazole synthesis by treating with amides. , However, a limited number of studies were done for thiazole synthesis from sec -propargyl alcohols as well as a couple of reports with tert -propargyl alcohols using silver triflate and p -toluenesulfonic acid . On the other hand, calcium salts have been identified as sustainable Lewis acid catalysts for various organic reactions due to their large abundance, biodegradability, non-toxic, less expensive, and moisture-stable features. , Over the past 5 years, our group has been actively engaged in utilizing the Ca­(II) catalysts for activating propargyl alcohols toward developing various synthetic methodologies . c With this experience, we desired to develop a catalytic, synthetic method for thiazole synthesis by treating propargyl alcohols and thioamides in the presence of a Ca­(II) catalyst, thereby extending this to the oxazole synthesis.…”