Palladium-catalyzed selective hydrogenolysis of alkenyloxiranes with formic acid. Stereoselectivity and synthetic utility

Selective hydrogenolysis of alkenyloxiranes to give homoallylic alcohols was carried out using formic acid in the presence of palladium-phosphine catalyst. The selectivity of the reaction depends on a nature and an amount of phosphine ligands. The reaction proceeds stereoselectively, because the hydride derived from formic acid attacks the allyl groups intramolecularly from a palladium side of π-allylpalladium hydride intermediates. The stereoselectivity of hydride attack, which induces the ring opening of alkenyloxiranes, can be controlled by the olefin geometry of alkenyloxiranes. Thus, inversion of configuration at the oxirane carbon by the hydride attack was observed in the reaction of (E)-alkenyloxiranes, whereas configuration at the oxirane carbon was retained with (Z)-alkenyloxiranes owing to the anti-syn isomerization of the π-allylpalladium system prior to the hydride attack. On the basis of these observations, both (S)- and (R)-6,10-dimethyl-2-undecanones were synthesized with high enantiomeric purities starting from one enantiomer, (2S,3S)-6,6-(2,2-dimethylpropylenedioxy)-2,3-epoxy-2-methyl-1-heptanol.