pi-Facial diastereoselection of hydride reduction of 1,3-diheteran-5-ones:Application of the exterior frontier orbital extension model

To obtain further evidence for the importance of the ground state conformat ional and orbital properties in pi -facial diastereoselection of 1,3-dihete ran-5-ones (heteroatom = O, S, Se), 2-phenyl-1,3-diselenan-5-one (3a) has b een synthesized, and its pi -facial diastereoselection upon hydride reducti on has been examined. The experimental data of pi -facial stereoselection o f 3a has been successfully rationalized by the exterior frontier orbital ex tension model (the EFOE model). Intrinsic reaction coordinate (IRC) and nat ural bond orbital (NBO) analyses of transition states of LiAlH4 reduction o f this ketone have strongly indicated that the transition state effects (th e torsional strain of the carbonyl moieties and the antiperiplanar effects involving the incipient bond proposed by the conventional theoretical model s for pi -facial diastereoselection; the Felkin-Anh model and the Cieplak m odel) are not responsible for facial selection. (C) 2001 John Wiley & Sons, Inc.