Copper(I)-Mediated and Microwave-Assisted C_aryl−O_carboxylic Coupling:  Synthesis of Benzopyranones and Isolamellarin Alkaloids

Metal-Catalyzed Routes for the Synthesis of Furocoumarins and Coumestans

“…Thasana and coworkers reported the preparation of the coumestan derivative 95 through the intramolecular lactonization, mediated by copper(I) thiophene-2-carboxylate under MW irradiation, of 2-(2-bromophenyl)-6-methoxybenzofuran-3-carboxylic acid 94 (Scheme 42) [141]. The same reaction took place employing substoichiometric CuI (0.5 equivalent), albeit in a remarkably lower yield (31%).…”

Microwaves in the Synthesis of Natural Products

“…The approach of Singh and Guiry [13] involves ring opening of epoxide 41 by the Grignard reagent derived from 2-(2-bromoethyl)-2-methyl-1,3-dioxolane, in the presence of CuI (10 mol%) at −78 • C, affording syn-diol 42 in 80% yield. This was treated with ZrCl 4 (10 mol%) in methanol under MW irradiation to give (1R,5S,7S)-5-methyl-7-vinyl-6,8-dioxabicyclo[3.2.1]octane (43) in 86% yield in addition to (S)-1-[(2R,6S)-6-methoxy-6-methyltetrahydro-2H-pyran-2-yl]prop-2-en-1-ol (44). Hydrogenation of 43 in the presence of a catalytic amount of Pd/C at 10 bar gave (+)-endo-brevicomin (39) in 95% yield with an enantiomeric excess (ee) of 98.5% (Scheme 19.9).…”

“…This was converted into a mixture of (+)-largazole (182) The lamellarins exhibit various biological activities and are potential drug candidates for the treatment of some forms of cancer and AIDS. Thasana et al [43] reported a simple and highly effective C-O carboxylic coupling reaction catalyzed by copper(I) salts to synthesize benzopyranones under MW irradiation. The synthesis of isolamellarin (193) started from 194, which was converted into the pyrrolo[2,1-a]isoquinoline carboxylic acid 195 in excellent yield.…”

Synthesis of fluorescent dibenzopyranones by the Diels-Alder reaction of 4-styrylcoumarins and N-phenylmaleimide and in situ aromatization using DDQ

“…11 Furthermore, dibenzopyranones occur naturally in many food sources including citrus fruits, herbs, and vegetables. 12 There are several methods available for the synthesis of dibenzopyranones, the most common being Suzuki cross-coupling reaction followed by Lewis acid [13][14][15][16] or metal 17 mediated lactonization. More…”