Palladium (0) -catalyzed alkylative cyclizations of alkynes and allenes containing electrophilic functional groups with organoboron reagents

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-l-ols and 3-cycloalken-l-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.