89677-81-6Relevant academic research and scientific papers
Selective oxymetalation of terminal alkynes via 6-endo cyclization: mechanistic investigation and application to the efficient synthesis of 4-substituted isocoumarins
Kita, Yuji,Yata, Tetsuji,Nishimoto, Yoshihiro,Chiba, Kouji,Yasuda, Makoto
, p. 6041 - 6052 (2018)
The cyclization of heteroatom-containing alkynes with π acidic metal salts is an attractive method to prepare heterocycles because the starting materials are readily available and the organometallic compounds are useful synthetic intermediates. A new organometallic species in the heterocyclization provides an opportunity to synthesize heterocycles that are difficult to obtain. Herein, we describe a novel cyclic oxymetalation of 2-alkynylbenzoate with indium or gallium salts that proceeds with an unusual regioselectivity to give isocoumarins bearing a carbon-metal bond at the 4-position. This new type of metalated isocoumarin provided 3-unsubstituted isocoumarins that have seldom been investigated despite their important pharmacological properties. Indium and gallium salts showed high performance in the selective 6-endo cyclization of terminal alkynes while boron or other metals such as Al, Au, and Ag caused 5-exo cyclization or decomposition of terminal alkynes, respectively. The metalated isocoumarin and its reaction intermediate were unambiguously identified by X-ray crystallographic analysis. The theoretical calculation of potential energy profiles showed that oxyindation could proceed via 6-endo cyclization under thermodynamic control while previously reported oxyboration would give a 5-membered ring under kinetic control. The investigation of electrostatic potential maps suggested that the differences in the atomic characters of indium, boron and their ligands would contribute to such a regioselective switch. The metalated isocoumarins were applied to organic synthetic reactions. The halogenation of metalated isocoumarins proceeded to afford 4-halogenated isocoumarins bearing various functional groups. The palladium-catalyzed cross coupling of organometallic species with organic halides gave various 4-substituted isocoumarins. A formal total synthesis of oosponol, which exhibits strong antifungal activity, was accomplished.
A concise synthesis of 3,4-fused spiro[isobenzofuran-3-ones], spiro[furo[3,4-b]pyridin-5(7H)-ones], 3-aryl-, and alkylphthalides
Kuethe, Jeffrey T.,Maloney, Kevin M.
, p. 5248 - 5258 (2013/06/27)
A synthetically useful protocol has been developed for the preparation of highly functionalized 3,4-fused spiro[isobenzofuran-3-ones], spiro[furo[3,4-b]pyridin-5(7H)-ones], 3-aryl-, and alkylphthalides. Reaction of 2-iodobenzoate esters and 2-iodopyridine carboxylate esters with i-PrMgCl·LiCl in the presence of cyclic ketones under standard Barbier reaction conditions affords 3,4-fused spiro[isobenzofuran-3-ones] and spiro[furo[3,4-b]pyridin-5(7H)-ones] in good to excellent yields. Step-wise addition of i-PrMgCl·LiCl to 2-iodobenzoate esters followed by trapping with various aldehydes yields 3-aryl and 3-alkylphthalides; whereas, under similar conditions access to 3-aryl and 3-alylazaphthalides is also possible. Extension of this methodology toward the preparation of 3-n-butylphthalide and chrycolide, a natural product isolated from the leaves and stems of Chrysanthemum coronarium, is also described.
