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.
Synthesis of 2-Phosphonopyrroles via a One-Pot RCM/Oxidation Sequence
作者:Kristof Moonen、Nicolai Dieltiens、Christian V. Stevens
DOI:10.1021/jo060160e
日期:2006.5.1
A four-step synthesis of 2-phosphonopyrroles is presented starting from suitable aldehydes. The key step in the synthesis involves a one-potring-closingmetathesis/oxidation sequence of a functionalized α-aminoalkenyl phosphonate. Notwithstanding the presence of a nucleophilic nitrogen atom and high substitution patterns in the substrate, the results of the RCM reaction are excellent using mild reaction
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
1,7-Electrocyclisations of 4-azaheptatrienyl lithium compounds to 4,5-dihydroazepines
作者:Stephanie Klötgen、Ernst-Ulrich Würthwein
DOI:10.1016/0040-4039(95)01480-6
日期:1995.9
6-heptatrienes 9, 10 at −78°C using lithium diisopropylamide as base yields 4-azaheptatrienyllithiumcompounds 11. During warming up to room temperature (to 40°C for 10) they undergo a 1,7-electrocyclisation to afford 3-azacycloheptadienyl lithiumcompounds 13. Subsequent treatment with various electrophiles provides access to several substituted 4,5-dihydroazepines 14.
Tandem Addition of Trialkyl Phosphites to α,β-Unsaturated Imines: A Comparison with Silylated Phosphites
作者:Ellen Van Meenen、Kristof Moonen、Annelies Verwée、Christian V. Stevens
DOI:10.1021/jo061256b
日期:2006.9.1
Trialkyl phosphites were evaluated for addition reactions to α,β-unsaturatedimines. An acidic medium is required to allow consecutive 1,4- and 1,2-addition to occur. In this manner, 3-phosphonyl-1-aminophosphonates, phosphonic acidanalogues of glutamate, are obtained in good yields (32−90%). The reaction is mainly influenced by the steric bulk of the nitrogen substituent: less steric N-substituents