Selectivities of trans-2-heterobicyclo [ 4 . 4 . 0 ] decan-5-ones in reductions with NaBH

The axial selectivities of 2-heterobicyclo[4.4.0]decan-5-ones decrease from the N-benzyl-2-azato 2-oxato 2-thiaspecies. This does not follow the earlier proposed Cieplak’s hypothesis of nheteroatom→σ*# interaction. It is rather dependent on the differential electron withdrawing abilities of the heteroatoms that translate further into differential σvicinal→π*C=O interactions in the ground states of the molecules. The heightened axial selectivity of the aza-species is probably due to hydrogen bonding of nitrogen with the solvent that enhances its electron withdrawing ability further.