Synthesis of β-lactams by condensation of titanium enolates of 2-pyridylthioesters with imines. Influence of the imine structure on the trans/cis stereoselectivity
摘要:
The condensation of the titanium enolates of C-2 alkyl substituted 2-pyridylthioesters with imines affords beta-lactams in trans/cis ratios that largely depend on the structure of the C-imine residue. Bulky and non-chelating heteroatom-containing groups lead to the formation of trans p-lactams, while sterically non-requiring or chelating groups favour the formation of the cia-products. On the basis of NMR evidences a rationale is proposed to account for the observed stereoselectivity.
The cyanosilylation of a series of N-substituted lactaldehyde imines is reported. The trimethylsilylcyanide addition affords optically active α-amino nitriles. All the imines show a syn diastereofacial selectivity that is maintained irrespective to the nature of the Lewis acid employed and even remains in the noncatalyzed reaction.