Rhodium‐Catalyzed Parallel Kinetic Resolution of Racemic Internal Allenes Towards Enantiopure Allylic 1,3‐Diketones

A rare case of a parallel kinetic resolution of racemic 1,3‐disubstituted allenes by means of a rhodium‐catalyzed addition to 1,3‐diketones furnishing enantiopure allylic 1,3‐diketones is described. Mechanistic experiments demonstrate that the different allene enantiomers react in parallel to either the diastereomeric E‐ or Z‐allylic 1,3‐diketones with the same absolute configuration of the newly formed stereogenic center. A broad substrate scope demonstrates the synthetic utility of this new method.     

Mechanism of the Thermal Z⇌E Isomerization of a Stable Silene; Experiment and Theory

The E and Z geometric isomers of a stable silene (tBu₂MeSi)(tBuMe₂Si)Si=CH(1‐Ad) ( 1 ) were synthesized and characterized spectroscopically. The thermal Z to E isomerization of 1 was studied both experimentally and computationally using DFT methods. The measured activation parameters for the 1Z ? 1E isomerization are: E_a=24.4 kcal mol^?1, ΔH^≠=23.7 kcal mol^?1, ΔS^≠=?13.2 e.u. Based on comparison of the experimental and DFT calculated (at BP86‐D3BJ/def2‐TZVP(‐f)//BP86‐D3BJ/def2‐TZVP(‐f)) activation parameters, the Z?E isomerization of 1 proceeds through an unusual (unprecedented for alkenes) migration–rotation–migration mechanism (via a silylene intermediate), rather than through the classic rotation mechanism common for alkenes.     

Palladium‐Catalyzed Chemo‐ and Enantioselective C−O Bond Cleavage of α‐Acyloxy Ketones by Hydrogenolysis

A chemoselective C−O bond cleavage of the ester alkyl side‐chain of α‐acyloxy ketones was realized for the first time by a highly efficient palladium‐catalyzed hydrogenolysis (S/C=6000, the highest catalytic efficiency by far). Furthermore, a kinetic resolution of α‐acyloxy ketones was first developed by enantioselective hydrogenolysis with good yields and up to 99 % ee.