Cerium(III) chloride-mediated reactions of sulfonamide dianions

Article abstract of DOI:10.1021/jo034001w

Presented here is the first report on the ability of cerium(III) chloride to mediate high-yielding and, oftentimes, highly diastereoselective additions of N-benzyl-α, N-dilithio methanesulfonamide to aldehydes and ketones of biological importance. Smooth addition was effected to base-sensitive substrates such as Fmoc-protected alaninal, citral, 5-cholesten-3-one, uridine 5′-aldehyde, 3′-ketouridine, and 3′-ketothymidine. The reaction was chemoselective for aldehydes in the presence of nitriles. Acetoxy groups are labile and thus not suitable protecting groups for alcohols under these conditions. N-Benzyl-α, N-dilithio methanesulfonamide was found to be of sufficient basicity to cause enolate formation with sensitive substrates, such as 1-phenylacetone. However, the addition of cerium(III) chloride mediated the basicity of the dianion and suppressed enolate formation in these cases. Further, cerium(III) has general utility for the addition of various N-aliphatic/aromatic methanesulfonamide dianions to 3′-ketouridine.