(Phenylsulfonyl)allenes as Substrates for Cycloaddition Reactions: Intramolecular Cyclizations onto Unactivated Alkenes
摘要:
The reaction of a series of allyl-substituted bis(phenylsulfonyl)methanes or dimethyl malonates with 2,3-bis(phenylsulfonyl)-1,3-butadiene in the presence of base afforded alkenyl-substituted allenes in good yield. The reaction proceeds by initial attack of the soft carbanion onto the terminal position of the diene, and this is followed by PhSO(2)(-) elimination to give the phenylsulfonyl-substituted allene. Themal [2 + 2]-cycloaddition proceeded across the C-1-C-2 double bond of the allene with completely sterospecificity. Stepwise bonding prefers to occur in a 1,6-exo manner rather than in a 1,7-endo fashion. Substitution at the 7-position of the pi-bond causes a crossover in the regioselectivity of the [2 + 2]-cycloaddition process. All products can be rationalized by a mechanism which includes an initial carbon-carbon bond formation involving the central allene carbon to give a diradical intermediate. The product distribution is then determined by the substitution pattern of the alkene and the fate of the diradical intermediate.
作者:Masanori Takimoto、Yoichi Nakamura、Kaoru Kimura、Miwako Mori
DOI:10.1021/ja049506y
日期:2004.5.1
A method for nickel-catalyzed asymmetric carbondioxide (CO2) incorporation via carbon-carbon bond formation was developed. In the presence of a catalytic amount of Ni(acac)2 and MeO-MOP, various bis-1,3-dienes reacted with CO2 (1 atm) and a diorganozinc reagent (Me2Zn or Ph2Zn) to afford cyclic carboxylicacids in good yields (71-100%) and with high enantioselectivities (90-96% ee).
Nickel-Catalyzed Enantioselective Three-Component Coupling of Bis-1,3-dienes, Aldehydes, and Dimethylzinc
作者:Masanori Takimoto、Yuuki Kajima、Yoshihiro Sato、Miwako Mori
DOI:10.1021/jo051283m
日期:2005.10.1
bis-1,3-dienes, aldehyde, and dimethylzinc was investigated. In the presence of catalytic amounts of Ni(acac)2 and PPh3, bis-1,3-dienes smoothly react with an aldehyde and dimethylzinc via intramolecular cyclodimerization of bis-1,3-diene moiety. The reaction proceeds through formation of a cyclic bis-allylnickel complex, insertion of an aldehyde, and addition of dimethylzinc to the resulting oxanickellacycle