Silylformylation of Chiral 1-Alkynes, Catalysed by Solvated Rhodium Atoms
摘要:
Solvated rhodium atoms, prepared by the metal vapour synthesis technique, promote the silylformylaton reaction of variously substituted alkynes (RRCH)-R-1-C-2(CH2)(n)C equivalent to CH, with catalytic activities comparable with and even higher than more common species such as Rh-4(CO)(12). Z-Silylalkenals are exclusively formed in high yields (60-95%) indicating syn addition both of CO and of the silane (Me2PhSiH) to the triple bond, The chemoselectivity of the process (silylformylation vs. hydrosilylation) is highly affected by the amount of catalyst employed (mmol of Rh species with respect to the alkyne reagent), by the steric requirements of the acetylenic substrates and by the hydrosilane/alkyne molar ratio. When optically active acetylenes are treated in the presence of Me2PhSiH under carbon monoxide pressure, the silylformylation reaction occurs with total retention of stereochemistry of the stereogenic centre, even if it is at the alpha -position of the unsaturated moiety, to afford enantiomerically enriched beta -silylalkenals.
New synthesis of α-benzylaldehydes from 2-(dimethylphenylsilylmethylene)alkanals by fluoride promoted phenyl migration
作者:Laura Antonella Aronica、Francesca Morini、Anna Maria Caporusso、Piero Salvadori
DOI:10.1016/s0040-4039(02)01178-4
日期:2002.8
α-Benzyl aldehydes are prepared from easily available β-silylalkenals and fluoride reagents, under mild experimental conditions; the reaction occurs instantaneously with almost quantitative yields. A plausible mechanism is suggested, which involves a 1,2-phenylmigrationfrom the silicon to the adjacent carbon atom.