Origin of π-facial stereoselectivity of hydride reduction of cyclohexanones. A new interpretation based on quantitative analysis of exterior frontier orbital extension

✍ Scribed by Shuji Tomoda; Takatoshi Senju

• Publisher: Elsevier Science
• Year: 1997
• Tongue: French
• Weight: 548 KB
• Volume: 53
• Category: Article
• ISSN: 0040-4020
• DOI: 10.1016/s0040-4020(97)00598-x

✦ Synopsis

A new theoretical interpretation for n-facial stereoselectivity of hydride reduction of cyclohexanones has been proposed based on the simple assumption that the lowest unoccupied molecular orbital (LUMO) of the substrates should play an essential role in the reaction: rt-Facial stereoselectivity is described by relative magnitude of exterior frontier orbital extension (EFOE) of the LUMO above or below the carbonyl plane, which is defined by integrated "hole-density" of the LUMO at the carbonyl carbon over three-dimensional spatial points outside repulsive molecular surface, where the absolute total value of the gaussian functions belonging to the carbonyl carbon makes the maximum contribution to the total value of the LUMO wave function so that the driving force vector on hydride is maximally directed toward the carbonyl carbon. A good linear correlation is observed for ten alkylsubstituted cyclohexanones (NaBH 4 in 2-propanol) between the difference in the square of EFOE 2 2 densities for the axial (EFOE(ax)) and equatorial (EFOE(eq)) areas (A = EFOE(ax) -EFOE(eq) ) and the difference in activation enthalpy for equatorial (AHCeq) and axial (AH~ax) attack (AAH~ = AHC~eq -AH~ax).