Daisuke Kaneno

Theoretical study on the mechanism and diastereoselectivity of NaBH4 reduction.

As the first step to understand the reaction mechanism and diastereoselectivity of sodium borohydride reduction of ketones, ab initio Car-Parrinello molecular dynamics simulation has been performed on a solution of NaBH4 in liquid methanol. According to pointwise thermodynamic integration involving constrained molecular dynamics simulations, it was strongly suggested that Na+ and BH4(-) are associated in the solvent forming contact ion pairs. Thus we propose a new transition state structure model that contains complexation of the carbonyl oxygen with sodium cation. Predicted diastereoselectivity of the reduction of some substituted cyclohexanones applying this novel transition state model is in good agreement with experimental data, showing its validity and effectiveness to investigate the diastereoselectivity of NaBH4 reduction of other ketones.

Intra- and intermolecular reaction selectivities of γ-substituted adamantanylidenes.

A study of adamantanylidenes having a γ-substituent (R) was undertaken to gauge how inductive and steric effects of remotely positioned functional groups influence intra- and intermolecular product selectivity. 3H-Diazirines were thermolyzed or photolyzed to generate the corresponding carbenes. On rapid heating, the resulting carbenes isomerized to 2,4-didehydroadamantanes by intramolecular 1,3-CH insertions. When R was an electron donor (R(D)) mostly asymmetric 1-substituted derivatives were produced but when it was an electron acceptor (R(A)) the symmetric 7-substituted ones were formed. When solutions were exposed to UV-A light, intermolecular adducts from the carbenes and solvent predominated with lesser amounts of intramolecular product being formed. Valence isomerization of 3H-diazirines also afforded diazo compounds. In methanol, protonation of diazo compounds to give the corresponding 2-adamantyl cations exceeds their coupling. This diversion was controlled with fumaronitrile by trapping the diazo compounds. The adducts possessed mostly anti configurations with R = R(D) and syn arrangements with R = R(A). The connection between as- and anti-product formation and that of s- and syn-products was deemed to be the consequence of a rapid equilibrium between two distinct carbene conformations. This was qualified and quantified using ab initio calculations and NBO analyses.

Reversal of π-facial diastereoselection in the hydride reduction of selenanones. Further application of the exterior frontier orbital extension model

Abstract Reversal of π-facial diastereoselection in the hydride reduction of 2-phenyl-4-selenanone ( 1b ) and 6-phenyl-3-selenanone ( 2b ) has been rationalized by the exterior frontier orbital extension model (EFOE model).