Palladium-mediated synthesis of 5-substituted 4-alkynylthieno[2,3-c]pyran-7-ones

Palladium-Catalyzed Alkynylation of Aryl and Hetaryl Halides: A Journey from Conventional Palladium Complexes or Salts to Palladium/Carbon

“…50 However, due to the further participation of terminal alkyne in this coupling-cyclization process, 4-alkynylthieno[2,3-c]pyran-7-ones 26 were isolated as major products in good yields. N,N-Dimethylformamide was identified as the solvent of choice in which the maximum yields of 26 were achieved.…”

“…It was observed that unlike the coupling reaction of oiodobenzoic acid, the one with 3-iodothiophene-2-carboxylic acid (25) with terminal alkynes in the presence of Pd(PPh 3 ) 2 Cl 2 -Et 3 N-CuI as a catalyst system afforded a six-membered ring product as a major product (Table 12). 50 However, due to the further participation of terminal alkyne in this coupling-cyclization process, 4alkynylthieno[2,3-c]pyran-7-ones 26 were isolated as major products in good yields. N,N-Dimethylformamide was identified as the solvent of choice in which the maximum yields of 26 were achieved.…”

Pd/C-mediated synthesis of α-pyrone fused with a five-membered nitrogen heteroaryl ring: A new route to pyrano[4,3-c]pyrazol-4(1H)-ones

“…A favorable geometry associated with the formation of the 5-6 ring over the 5-5 ring did not allow the intermediate alkyne Z to undergo a 5- exo-dig ring closure though it is favoured by Baldwin’s rules. Unlike 3-iodo thiophene-2-carboxylic acid [ 18 ] the coupling of 1 with terminal alkynes 2 in the presence of PdCl 2 (PPh 3 ) 2 and CuI did not provide the 7-alkynyl substituted derivative of 3 possibly due to the “peri” effect caused by the N-1 methyl group of the pyrazole ring.…”

“…Thus, isocoumarins have been prepared by reacting o -iodobenzoic acid with terminal alkynes in the presence of a Pd-catalyst [ 14 – 16 ]. Recently, we have reported synthesis of thienopyranones following a similar strategy [ 7 , 18 ]. On the other hand construction of a pyridine ring on a pyrazole moiety has been described under Ni or Pd catalysis [ 19 ].…”

Rhodium(III)‐Catalyzed Formal Cycloaddition between Thienopyridine/Thienopyrazine Carboxylic Acids and Alkynes, Triggered by C−H Activation

“…Thiophene fused bicyclic or tricyclic ɑ‐pyrones were earlier prepared by Pal et al [3a–c] . and Queiroz et al ., [4a,b] by reaction between ɑ‐halothiophene derivatives bearing carboxylic acids or methyl esters, and terminal alkynes, using a Pd/Cu‐catalyzed Sonogashira coupling followed by (halo)electrophilic cyclization.…”