Ag2CO3-catalyzed difunctionalization of alkynes via a radical phosphonation and C-H functionalization tandem process was developed to synthesize various 3-phosphonated coumarins in moderate to high yields with high regioselectivity. A catalytic amount of cheap and nontoxic silver salt was employed in the domino C-P and C-C formation of alkynoates for the first time. Mechanistic studies indicate that the reaction pathway might proceed via the generation and cyclization of a phosphonated vinyl radical intermediate.
A novel Pd(II)-catalyzed dehydrogenative cross-coupling reaction between coumarins and H-phosphonates has been developed to give the corresponding 3-phosphonated products in moderate to good yields with high selectivity.
The direct ring construction of amides with alkynes catalyzed by palladium acetate with cheap oxidant under an air atmosphere has been realized. A variety of novel highly substituted naphthalenes 3a-3l have been prepared chemo- and regioselectively in 55-97% yields under mild conditions. Product 3j emits intense blue luminescence peaked at 435 nm with a good blue purity.
A new and efficient metal-free tandem acylation/cyclization of alkynoates with aldehydes was developed for the synthesis of 3-acyl-4-arylcoumarins. The reaction was achieved by the addition of acyl radical to alkynes and a C-H bond functionalization to form two new C-C bonds simultaneously.
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