Base catalysed cyclization of 1-(2′-hydroxy-phenyl)-2-ynones: A new pathway to the chromone skeleton.

Cascade Reactions: Sequential Homobimetallic Catalysis Leading to Benzofurans and β,γ‐Unsaturated Esters

“…Free phenols 3, however, with R 2 = alkyl, were, according to the literature, difficult to obtain in the pure state owing to their instability and tendency to polymerize. [7] This was confirmed by our attempts to prepare 2-(1-hydroxyhept-2-ynyl)phenol (R 1 = H, R 2 = Bu), which were unsuccessful. One possibility to bypass this inconvenience was to protect the phenolic À OH group with a suitable function, removable in situ under the reaction conditions.…”

Cascade Reactions: A New Synthesis of 2-Benzofuran-2-ylacetamides by Sequential Pd(0)-Catalyzed Deallylation−Pd(II)-Catalyzed Aminocarbonylative Heterocyclization of 1-(2-Allyloxyaryl)-2-yn-1-ols

“…The GLC−MS analysis of the reaction crude also suggested the presence in the reaction mixture of the deallylated substrate, that is, the free phenol 2a (R 1 = R 3 = R 4 = R 5 = H, R 2 = Bu, ca. 30%), which, however, according to its instability, could not be isolated at the pure state from the reaction crude. The formation of unidentified heavy compounds was detected by TLC analysis (these materials were chromatographically immobile) and accounted for the remaining part of the converted substrate.…”

“…Thus, 1-(2-allyloxyaryl)-2-yn-1-ols 1 were selectively converted into 2-benzofuran-2-ylacetic esters 3 through Pd(0)-catalyzed carbonylative deallylation to give β,γ-unsaturated esters and the free phenols 2 , followed by in situ PdI 2 -catalyzed cyclization−alkoxycarbonylation of the latter to give 3 , as depicted in Scheme (unreactive ligands are omitted for clarity). The possibility to obtain free phenols 2 in situ, by deallylation of 1 , was particularly important, since phenols 2 , with R 2 = alkyl, were known to be unstable and therefore difficult to obtain at the pure state . On the other hand, the use of isolable phenols 2 (with R 2 = H or aryl) led to the corresponding benzofurans 3 in lower yields with respect to the sequential procedure starting from O -allyl phenols 1 .…”

“…The possibility to obtain free phenols 2 in situ, by deallylation of 1, was particularly important, since phenols 2, with R 2 ) alkyl, were known to be unstable and therefore difficult to obtain at the pure state. 2 On the other hand, the use of isolable phenols 2 (with R 2 ) H or aryl) led to the corresponding benzofurans 3 in lower yields with respect to the sequential procedure starting from O-allyl phenols 1. Reactions were carried out in MeOH at 100 °C under 30-90 atm of carbon monoxide in the presence of catalytic amounts of PdI 2 (1 mol % with respect to 1) in conjunction with 100-200 equiv of KI, 4 equiv of PPh 3 , and 200 equiv of H 2 O.…”