193148-89-9Relevant academic research and scientific papers
A chiral, oxidatively cleavable auxiliary in β-lactam synthesis - Double diastereocontrol with p-methoxyphenethyl-substituted imines
Podlech, Joachim,Steurer, Steffen
, p. 650 - 654 (2007/10/03)
A new chiral, oxidatively removable auxiliary for the Staudinger reaction is presented. When diazo ketones 1-3 prepared from suitably protected amino acids reacted with p-methoxyphenethyl (PMPE)-substituted imines, the corresponding trans-substituted β-lactams 7 and 8a-h were formed. With the (S)-configured imine 5, an improvement of the selectivities is observed in comparison with achiral p-methoxybenzyl (PMB)-substituted imines by double stereoselection; consequently, the ratio of isomers decreased with the (R)-imine 4. The auxiliary could be removed with cerium ammonium nitrate (CAN).
Cycloadditions of Ketenes Generated in the Wolff Rearrangement. Stereoselective Synthesis of Aminoalkyl-Substituted β-Lactams from α-Amino Acids
Podlech, Joachim,Linder, Michael R.
, p. 5873 - 5883 (2007/10/03)
Diazo ketones 1-16, derived from suitable protected amino acids (Ala, Leu, Val, Ile, Tie, Phe, Pro, Orn, Lys, Ser, and Thr), have been photochemically rearranged, leading to the corresponding ketene intermediates. They were trapped with N-benzylbenzaldimine 17 to give β-lactams 18-33 in up to 90% yield. In these cycloadditions, two of the four possible diastereoisomers were formed exclusively. The selectivity ranged from 60:40 to 93:7 and the bulkiness of the parent amino acid side chain is the governing factor. The relative configuration was proved by three X-ray crystal structures. The diastereoselectivity in these reactions is also influenced by the use of chiral N-phenethylbenzaldimines 34 and 35. With regard to a projected deprotection of the lactam-nitrogen, N-allyl- (49) and N-(p-methoxybenzyl)benzaldimme (44) were used in this reaction. This led to the N-allyl β-lactams 50 and 51 in 62 and 56% yield, respectively, and to the p-methoxybenzyl-substituted β-lactams 45 and 46 (50 and 72% yield). The p-methoxybenzyl group on the valine-derived β-lactam 45a can be cleaved with potassium peroxodisulfate in 63% yield.
