Intramolecular Enantioselective Palladium-Catalyzed Heck Arylation of Cyclic Enamides

Abstract

Palladium-catalyzed intramolecular cyclization of N-formyl-6-[3-(2-iodophenyl)propyl]-1,2,3,4-tetrahydropyridine (1a) and N-formyl-6-[2-(2-iodophenyl)ethyl]-1,2,3,4-tetrahydropyridine (1b) in the presence of AsPh(3) resulted in formation of the spiro compounds N-formyl-3,3',4,4'-tetrahydrospiro[naphthalene-1(2H),2'(1'H)-pyridine] (2a) and N-formyl-3',4'-dihydrospiro[indan-1,2'(1'H)-pyridine] (2b), respectively, and in the presence of PPh(3) and TlOAc in the spiro compounds N-formyl-3,4,5',6'-tetrahydrospiro[naphthalene-1(2H),2'(1'H)-pyridine] (3a) and N-formyl-5',6'-dihydrospiro[indan-1,2'(1'H)-pyridine] (3b), respectively. Cyclization of N-formyl-6-(3-{2-[(trifluoromethanesulfonyl)oxy]phenyl}propyl)-1,2,3,4-tetrahydropyridine (7) in presence of a chiral (phosphinoaryl)oxazoline ((S)-8) resulted in formation of (R)-3a and (R)-N-formyl-1',3,4,6'-tetrahydrospiro[naphthalene-1(2H),2'(3'H)-pyridine] ((R)-6a) in high enantiomeric excesses, 87% and >99%, respectively, and in good yield. The oxazoline ligand (S)-8 furnished higher enantiomeric excesses and improved regioselectivities than (R)-BINAP.

Solvent-modulated Pd/C-catalyzed deprotection of silyl ethers and chemoselective hydrogenation

“…While TIPS (1d) and TBDPS ethers (1e) were stable under hydrogenation conditions using Pd/C even in MeOH (entries 4 and 5), TES (1b) and TPS ethers (1c) were completely deprotected in MeOH as well as the TBDMS ether (1a) (entries 1-3). The cleavage of silyl ethers was apparently depressed in aprotic solvents such as THF and EtOAc (entries 6 -8 and 11-13) and silyl ethers were nearly stable in MeCN (entries [16][17][18]. Although a small amount of TBDMS deprotection was observed in THF, it was entirely stable in AcOEt and MeCN (compare entries 6 with 11 and 16).…”

Intermolecular Heck Reaction: Scope, Mechanism, and Other Fundamental Aspects of the Intermolecular Heck Reaction

“…[20] For selective internal arylation of vinyl ethers with aryl iodides or bromides for which cationic organopalladium intermediates are required as intermediates, thallium salts are utilized as additives. [34] Although the role of the thallium additives [87]- [90] (or silver additives) [91]- [96] has not been fully elucidated, it is likely that these additives act as halide sequestering agents. Upon addition of thallium acetate, the halide ion in the oxidative addition complex is replaced by the acetate (X ϭ OAc).…”

Síntese de indanos: uma seleção de métodos gerais e eficientes

“…Esta ciclização foi realizada na presença de um composto de arsênio ou na de acetato de tálio e trifenilfosfina, sendo que estes últimos suprimiram a isomerização da dupla ligação, fornecendo o indano 35 35 (Esquema 25). Um outro exemplo de ciclização intramolecular catalisada por paládio foi descrito por Crousse et al 36,37 , que utilizaram o complexo de haloareno-crômio 36 como material de partida para preparação de indanos oticamente ativos.…”