Diazoketones as precursors in β-lactam synthesis. New insights into the mechanism of the photochemically induced Staudinger reaction
作者:Michael R. Linder、Wolfgang U. Frey、Joachim Podlech
DOI:10.1039/b105748k
日期:2001.10.11
Diazoketones 1â3, derived from suitably protected amino acids (Ala, Val and Tle), have been photochemically rearranged in the presence of imines leading exclusively to trans-arranged 4-aryl- and cinnamoyl-substituted β-lactams 17â33 with up to 84% yield. Selectivities were dependent on the steric demand of the amino acid side-chain ranging from 65 â¶ 35 to 90 â¶ 10. The relative configurations were proved by several X-ray crystal structures and comparison of NMR spectra. Further reactions of the azetidinones at position C-4 have been performed: electron-rich aryl substituents (e.g., 4-methoxyphenyl, furyl and thienyl) could be degraded to carboxylic
acids 34 and 35 which were further transformed to acetoxy derivatives (compounds 36 and 37) in a Kolbe reaction of type II. The cinnamoyl group could be oxidized to the formyl group by ozonolysis (â
38, 39). The mechanism of the photochemically induced β-lactam formation is discussed in detail.
Enantioselective Organocatalysis of Strecker and Mannich Reactions Based on Carbohydrates
作者:Christian Becker、Christine Hoben、Horst Kunz
DOI:10.1002/adsc.200600370
日期:2007.2.5
Efficient organocatalysts for enantioselective Strecker and Mannichreactions were constructed from glucosamine as a readily accessible chiral scaffold. A variety of aromatic aldimines were subjected to hydrocyanation with good to excellent yield (72–98 %) and, in part, high enantioselectivity (69–95 % ee). Influence of the catalyst architecture on the enantioselectivity obviously arises from restrictions
An Effective Method To Prepare Imines from Aldehyde, Bromide/Epoxide, and Aqueous Ammonia
作者:Jing-Mei Huang、Jue-Fei Zhang、Yi Dong、Wen Gong
DOI:10.1021/jo102455q
日期:2011.5.6
three-component reaction of aldehydes, alkyl bromides, and ammonia to form imines was studied. Aqueous ammonia was applied as the nitrogen source and solvent in the reaction. For the aromatic aldehyde, the product yields are good to excellent and the reaction conditions are mild to be compatible with a range of functional groups. The reaction of aldehydes and aqueous ammonia with epoxides was also studied and
Synthesis of Tricyclic Phosphonopyrrolidines via IMDAF: Experimental and Theoretical Investigation of the Observed Stereoselectivity
作者:Diederica D. Claeys、Kristof Moonen、Bart I. Roman、Victor N. Nemykin、Viktor V. Zhdankin、Michel Waroquier、Veronique Van Speybroeck、Christian V. Stevens
DOI:10.1021/jo801138s
日期:2008.10.17
During the synthesis of tricyclic phosphonopyrrolidines via intramolecular Diels-Alder reactions of 1-acylamino(furan-2-yl)methyl phosphonates, two isomers are formed in most cases. The presence of a short three-atom tether together with spectroscopic data, including difference NOE, revealed that the cycloaddition occurred exo, but the phosphonate substituent on the tether had an exo or endo orientation
Synthesis of β-Lactams from Diazoketones and Imines: The Use of Microwave Irradiation
作者:Michael R. Linder、Joachim Podlech
DOI:10.1021/ol015891+
日期:2001.6.1
[GRAPHICS]The transformation of diazoketones derived from alpha -amino acids to ketenes that, in turn, react further with imines to afford beta -lactams, can be realized not only by utilizing photochemical reaction conditions but also under the action of microwave irradiation. Under the latter reaction conditions 4-alkenyl substituted beta -lactams derived from amino acids, substrates that were not previously accessible, have been prepared. beta -actams possessing a trans-substitution pattern at the ring were obtained exclusively.