0価パラジウム触媒と有機ホウ素試薬を用いた分子内求電子剤を有するアルキン・アレンの付加・環化反応

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We have developed palladium(0)/monophosphine-catalyzed trans-selective alkylative cyclization reactions of alkyne- and allene-aldehydes with organoboron reagents leading to 3-substituted 2-cycloalken-1-ols and 3-cycloalken-1-ols, respectively. Three-component reaction involving secondary aliphatic amines as the third component affords the corresponding tertiary amines via in situ generated iminium ions. These cyclization reactions allow a combinatorial synthesis of biologically important indenes bearing three different substituents at 1,2,3-positions from available o-ethynylbenzaldehyde derivatives. 6-Endo-trig cyclizations of alkynyl- and allenyl-iminium ions, in situ prepared from 3-butynylamine and 2,3-butadienylamine with formaldehyde, afford 1,4-disubstituted 1,2,3,6-tetrahydropyridines. The remarkable trans-selectivity of these processes would result from the novel reaction mechanism involving “anti-Wacker”-type oxidative addition. Changes of the cyclization mode when enones were employed as electrophiles suggest that low tendency of palladium(0) catalyst to form π-complex with carbonyls and iminium ions cause the trans-selectivity.