Diastereoselective Michael Additions of Chiral Imidazolidines to Trityl Enones

The enolates A and C of t ‐butyl ( R )‐2‐ t ‐butyl‐3‐methyl‐4‐oxo‐1‐imidazolidinecarboxylate ( 1 , Boc‐BMI) and of 1‐ t ‐butyl 5‐methyl (2 R ,5 S )‐2‐ t ‐butyl‐3‐methyl‐1,5‐imidazolidinedicarboxylate ( 3 ) and t ‐butyl ( R )‐2‐ t ‐butyl‐5‐lithio‐3‐methyl‐1‐imidazolidinecarboxylate ( B , from 2 ) add in a Michael‐type reaction to trityl enones ( E, 4, 5 ). With one exception (product 8 ) a single diastereoisomer is formed (≫98% ds). — In two cases ( 6, 10 ), the crystal structures of the products are determined by X‐ray diffraction. The steric course of the reactions (the relative topicity is unlike with the enolates) is discussed and compared with that of other conversions of the same reagents. — The trityl groups of two adducts ( 8 and 9 ) are cleaved off by treatment with LiBH 4 /cat. LiBHEt 3 to give diaminopentanol derivatives ( 12 and 13 ).