title: Metal-catalyzed chemoselective cycloisomerization of cis-2,4-dien-1-als to 3-cyclopentenones and 4-alkylidene-3,4-dihydro-2H-pyrans.
abstract: [reaction: see text] PtCl(2) (5 mol %) catalyst effected cycloisomerization of cis-2,4-dien-1-al (1) to 3-cyclopentenone (3) efficiently in hot toluene. In the presence of p-TSA, this PtCl(2) catalysis gave 2-cyclopentenone (5) exclusively because of the secondary isomerization reaction. Although the 1-2 equilibrium state greatly favors aldehyde (1), PdCl(2)(PhCN)(2) (5 mol %) catalyzed cycloisomerization of aldehyde (1) to 4,6,7,8-tetrahydro-3H-isochromene (4) smoothly in hot toluene. A plausible mechanism is proposed on the basis of reaction observation and isotope-labeled experiment.
authors.affiliation: Department of Chemistry, National Tsing-Hua University, Hsinchu, Taiwan, Republic of China.
authors.forename: Ching-Yu
authors.initials: CY
authors.lastname: Lo
authors.forename: Chung-Chang
authors.initials: CC
authors.lastname: Lin
authors.forename: Hsin-Mei
authors.initials: HM
authors.lastname: Cheng
authors.forename: Rai-Shung
authors.initials: RS
authors.lastname: Liu