One-pot two-step synthesis of 3-iodo-4-aryloxy coumarins and their Pd/C-catalyzed annulation to coumestans

Abstract

An efficient protocol for the synthesis of various coumestans from the intramolecular annulation of 3-iodo-4-aryloxy coumarins through C–H activation has been developed.

Copper-catalyzed intramolecular cross dehydrogenative coupling approach to coumestans from 2′-hydroxyl-3-arylcoumarins

“…Further screening of the solvent ratio revealed that DMSO/H 2 O (3 : 1, v/v) gave the best result, whereas the 1 : 1, 2 : 1 or 4 : 1 (v/v) solvent ratio was less effective (compare entries 5-8). Subsequently, different oxidants were investigated, reaction performed under air gave similar result as under oxygen atmosphere (compare entries 5 and 9), other oxidants such as DTBP, TBHP, AgOAc, Ag 2 CO 3 and Cu(OAc) 2 in 2-3 equivalent amount respectively, could also promote the reaction, but lower yields were obtained (entries [10][11][12][13][14]. The choice of 1,10-phen as ligand was crucial for this reaction, other Scheme 2 Retrosynthetic analysis of coumestans 1.…”

Palladium-Catalyzed Weakly Coordinating Lactone-Directed C–H Bond Functionalization of 3-Arylcoumarins: Synthesis of Bioactive Coumestan Derivatives

“…The title compound 9f was synthesized following method E. The crude product was purified by using 1.0:9.0 ethyl acetate/hexane as an eluent: R f = 0.8; white solid (35 mg, 67%); mp = 158–160 °C (lit . mp 166–168 °C); 1 H NMR (400 MHz, CDCl 3 ) δ 8.04–8.00 (m, 2H), 7.64–7.59 (m, 1H), 7.53–7.48 (m, 2H), 7.44–7.40 (m, 1H), 7.31–7.29 (m, 1H), 2.56 (s, 3H); 13 C­{ 1 H} NMR (100 MHz, CDCl 3 ) δ 159.6, 158.2, 156.0, 153.5, 137.5, 131.6, 126.6, 124.6, 121.7, 121.3, 120.8, 117.4, 112.8, 112.0, 105.9, 21.9; HRMS (ESI) m / z [M + H] + calcd for C 16 H 11 O 3 + 251.0703, found 251.0681.…”

“…37 38 The title compound 9f was synthesized following method E. The crude product was purified by using 1.0:9.0 ethyl acetate/hexane as an eluent: R f = 0.8; white solid (35 mg, 67%); mp = 158−160 °C (lit. 38 2-Methoxy-6H-benzofuro[3,2-c]chromen-6-one (9g). 39 The title compound 9g was synthesized following method E. The crude product was purified by using 1.5:8.5 ethyl acetate/hexane as an eluent: R f = 0.6; white solid (38.5 mg, 69%); mp = 154−156 °C (lit.…”

Exciting progress in the transition metal‐catalyzed synthesis of oxepines, benzoxepines, dibenzoxepines, and other derivatives

“…Wang et al in 2021 presented an electrooxidative Rh-catalyzed [5 + 2] annulation in an undivided cell setup equipped with graphite felt anode and platinum plate cathode to afford substituted benzoxepine 394 structure via C-H/O-H activations (Scheme 97). [143] S C H E M E 8 1 The proposed mechanism for the Fe-catalyzed synthesis of dibenzo[b,f]oxepine 356 S C H E M E 8 2 Fe-catalyzed synthesis of dibenzo[b,e]oxepin-11(6H)-one 362 S C H E M E 8 0 Fe-catalyzed synthesis of 8-phenyl-6H-benzo [6,7]oxepino [3,2-c]chromen-6-one 360 [119] S C H E M E 8 4 The proposed mechanism for the Fe-catalyzed synthesis of compounds 366 and 367 The possible mechanism is shown in Scheme 98. This strategy is the first electrocatalyzed [5 + 2] annulation for the construction of valuable seven-membered benzoxepine.…”