Intramolecular carbenoid ylide forming reactions of 2-diazo-3-keto-4-phthalimidocarboxylic esters derived from methionine and cysteine

• Marc Enßle,
• Stefan Buck,
• Roland Werz and
• Gerhard Maas

Beilstein J. Org. Chem. 2012, 8, 433–440, doi:10.3762/bjoc.8.49

• reaction. Keywords: α-aminoacids; carbonyl ylides; cycloaddition; α-diazo-β-ketoesters; sulfonium ylides; Introduction The synthetic potential of diazo compounds, in particular of α-diazoketones and α-diazoesters, is greatly widened by the ability of the derived carbene or metal-carbene intermediates to

• Synthesis of diazoesters The 2-diazo-3-oxo-4-phthalimidocarboxylic esters 8a–c were prepared from L-methionine (5a), S-benzyl-L-cysteine (5b) and S-allyl-L-cysteine (5c), respectively, in a three-step sequence (Scheme 3) applied by us previously for other α-aminoacids [18]. Acids 5a–c were converted into

• , so that the reaction could be performed in toluene under reflux. For phenylalanine, it was reported that no racemisation occurred under these conditions [21]. However, with some other α-aminoacids we have noted a small degree of racemisation [18]. In this work, we can confirm the reported specific