157639-16-2Relevant academic research and scientific papers
6-Endo- and 5-exo-digonal cyclizations of o-hydroxyphenyl ethynyl ketones: A key step for highly selective benzopyranone formation
Nakatani, Kazuhiko,Okamoto, Akimitsu,Saito, Isao
, p. 9427 - 9446 (2007/10/03)
The cyclization of o-hydroxyphenyl ethynyl ketones was examined from theoretical and experimental standpoints in order to develop efficient synthetic methods for the construction of 2-substituted pyranones possessing significant biological activities. Ab initio studies at HF/6-31G* level on the cyclization indicated that both 6-endo-digonal and 5-exo-digonal cyclizations giving benzopyranones and benzofuranones, respectively, were endothermic and reversible in aprotic media, and the irreversible protonation of the resulting unions would be critical for the products formation. We generated phenoxide ion under aprotic conditions in situ by desilylation of o-silyloxyphenyl ethynyl ketones with spray dried potassium fluoride and 18- crown-6 in anhydrous DMF. Under these conditions the cyclization of variety o-hydroxyphenyl ethynyl ketones proceeded smoothly to produce benzopyranone derivatives with exceedingly high selectivity. Theoretical and experimental results strongly suggested that the presence of a small amount of proton donor effecting the protonation of the resulting benzopyranone union was essential for the high 6-endo-diagonal selectivity.
Highly efficient synthesis of 2-substituted 4H-chromen-4-ones by means of F--induced 6-endo-digonal cyclization of o-(silyloxy)phenyl ethynyl ketone derivatives
Nakatani,Okamoto,Yamanuki,Saito
, p. 4360 - 4361 (2007/10/02)
Efficient synthesis of 2-substituted 4H-chromen-4-ones, a core structure of the antitumor antibiotic kapurimycin A3, was achieved through F-- induced cyclization of o-(silyloxy)phenyl ethynyl ketone derivatives.
