Synthesis of orthogonally protected biaryl amino acid derivatives
作者:Eduardo Moreno、Luca Antonio Nolasco、Lorenzo Caggiano、Richard F. W. Jackson
DOI:10.1039/b609360d
日期:——
The efficient and direct synthesis of protected biaryl amino acids, including dityrosine (50% overall yield over 3 steps), by Negishi cross-coupling of the serine-derived organozinc reagent 4 with iodo- and di-iodobiaryls, is reported. An improved, although still not perfect, diiodination of 2,2′-biphenol has been achieved using NMe3BnICl2–ZnCl2. Protection of phenolic hydroxyl groups as acetates, rather than benzyl ethers, is required for efficient cross-coupling, and evidence for acetyl migration has been observed during debenzylation of a substituted 2-acetoxy-2′-benzyloxybiaryl. Aromatic C–I to C–Cl conversion has been detected as a minor reaction pathway in the palladium-catalyzed coupling of aryl iodide 3b with organozinc reagent 4.
Synthesis of bis-α-amino acids through proline catalyzed asymmetric α-amination of higher homologs of Garner's aldehyde
作者:Ramu Petakamsetty、Ram Pada Das、Ramesh Ramapanicker
DOI:10.1016/j.tet.2014.10.048
日期:2014.12
A very convenient synthesis of bis-α-amino acids from the higher homologs of Garner's aldehyde is reported. The key step is proline catalyzed asymmetric amination of the aldehydes using dibenzylazodicarboxylate. The aldehydes used are either commercially available or can easily be prepared from aspartic or glutamic acid. One of the two chiral centers in the bis-amino acids comes from the aldehyde and
Evidence for the Role of Tetramethylethylenediamine in Aqueous Negishi Cross-Coupling: Synthesis of Nonproteinogenic Phenylalanine Derivatives on Water
作者:Andrew J. Ross、Frank Dreiocker、Mathias Schäfer、Jos Oomens、Anthony J. H. M. Meijer、Barry T. Pickup、Richard F. W. Jackson
DOI:10.1021/jo102334c
日期:2011.3.18
ne (TMEDA) cluster cation 3 has been determined in the gasphase by a combination of tandem mass spectrometry, infrared multiphoton dissociation (IRMPD) spectroscopy, and DFT calculations. Both sets of experimental results establish the existence of a strongly stabilizing interaction of TMEDA with the zinc cation. High-level DFT calculations on the alkylzinc−TMEDA cluster cation 3 allowed the identification