Showing papers by "Hiroaki Sasai published in 2019"
TL;DR: A method for the highly regio- and enantioselective oxidative coupling of resorcinols has been established by using dibrominated dinuclear vanadium(V) catalyst 1c under air.
Abstract: A method for the highly regio- and enantioselective oxidative coupling of resorcinols has been established by using dibrominated dinuclear vanadium(V) catalyst 1c under air. When resorcinols bearing an aryl substituent were applied as substrates to the coupling, axially chiral biresorcinols were obtained as single regioisomers in high yield with up to 98% ee.
23 citations
TL;DR: The first example of an asymmetric cyclization-dimerization of (ortho-alkynyl phenyl) (methoxymethyl) sulfides with a palladium(II) bisoxazoline (box) catalyst has been developed and the characteristic properties of the box ligand were supported by density functional theory (DFT) calculations of the intermediate.
Abstract: The first example of an asymmetric cyclization-dimerization of (ortho-alkynyl phenyl) (methoxymethyl) sulfides with a palladium(II) bisoxazoline (box) catalyst has been developed. The box ligand enhances the alkynophilicity of benzothienyl palladium(II) intermediate A and thus promotes coordination of the second alkyne substrate, leading to the dimerization. The characteristic properties of the box ligand were supported by density functional theory (DFT) calculations of the intermediate. Axially chiral bibenzothiophenes were obtained in good yields with good enantioselectivities.
14 citations
TL;DR: The Mills reaction and cyclization of readily available 2-aminobenzyl alcohols and nitrosobenzenes using thionyl bromide provided 2H-indazoles in up to 88 % yields and in the metal-free process, acetic acid played a crucial role for the both Mills Reaction and Cyclization.
Abstract: The Mills reaction and cyclization of readily available 2-aminobenzyl alcohols and nitrosobenzenes using thionyl bromide provided 2H-indazoles in up to 88 % yields. In the metal-free process, acetic acid played a crucial role for the both Mills reaction and cyclization. A brominated 2H-indazole could also be obtained through the one-pot sequence.
10 citations
TL;DR: The first total synthesis of (-)-graminin A is described, a palladium-catalyzed asymmetric cyclization carbonylation of prochiral propargylic acetate and copper complex mediated aldol condensation of (+)-gregatin B bearing a diene moiety.
Abstract: The first total synthesis of (-)-graminin A is described. Key features of our synthetic approach involve a palladium-catalyzed asymmetric cyclization carbonylation of prochiral propargylic acetate, conversion of the orthoester product into methyl 4-oxo-3-furancarboxylate, and copper complex-mediated aldol condensation of (+)-gregatin B bearing a diene moiety. A new synthesis of (+)-gregatin B and the first synthesis of (-)-graminin A were achieved.
6 citations