Erlenmeyer-Plochl reaction

The starting material for the enantioselective hydrogenation is obtained very elegantly by an Erlenmeyer-Plochl reaction ofvaniUm, N-acetylglycine and acetic anhydride. The azlactone is carefuUy hydrolysed with water and the enamide purified by crystallisation. 

The azlactones of a-benzoylaminocinnamic acids have traditionally been prepared by the action of hippuric acid (1, Ri = Ph) and acetic anhydride upon aromatic aldehydes, usually in the presence of sodium acetate. The formation of the oxazolone (2) in Erlenmeyer-Plochl synthesis is supported by good evidence. The method is a way to important intermediate products used in the synthesis of a-amino acids, peptides and related compounds. The aldol condensation reaction of azlactones (2) with carbonyl compounds is often followed by hydrolysis to provide unsaturated a-acylamino acid (4). Reduction yields the corresponding amino acid (6), while drastic hydrolysis gives the a-0X0 acid (5). ... 

A variant of the Perkin reaction is the Erlenmeyer-Plochl-azlactone synthesis By condensation of an aromatic aldehyde 1 with an N-acyl glycine 5 in the presence of sodium acetate and acetic anhydride, an azlactone 6 is obtained via the following mechanism ... 

Brooks, D. A. Erlenmeyer—Plochl Azlactone Synthesis in Name Reactions in Heterocyclic Chemistry, Li, J. J. Corey, E. J., Eds. Wiley Sons Hoboken, NJ, 2005, 229-233. (Review). 

Erlenmeyer-Plochl azlactone and amino acid synthesis. Formation of azlactones by intramolecular condensation of acylglycines in the presence of acetic anhydride. The reaction of azlactones with carbonyl compounds followed by hydrolysis to the unsaturated a-acylamino acid and by reduction yields the amino acid drastic hydrolysis gives the a-oxo acid. 

This reaction is related to the Erlenmeyer-Plochl Azlactone Synthesis. 

Erdmann (see Volhard-Erdmann Cyclization) Erlenmeyer-Plochl Azlactone and Amino Acid Synthesis Eschenmoser Coupling Reaction Eschenmoser Fragmentation Eschenmoser-Claisen Rearrangement Eschenmoser-Tanabe Fragmentation Eschweiler-Clarke Reaction Etard Reaction... 

The preparation of the first unsaturated azlactone was reported in 1883 by Plochl/40 who condensed benzaldehyde with hippuric acid in presence of acetic anhydride. This approach was later used by Erlenmeyer/41 who extended the procedure to include other aldehydes and also established the usefulness of azlactones as intermediates in the synthesis of DHAs. The method involves the condensation of an A-acylglydne 4 with aldehydes and ketones in the presence of acetic anhydride and anhydrous sodium acetate (Scheme 2)J41 t5l Other catalysts such as copper(II) acetate/46 lead acetate/47,48 potassium carbonate/49 or potassium hydrogen carbonate 50 have also been used. The reaction proceeds via formation of an azlactone 5, which then condenses with the appropriate aldehyde or ketone to give unsaturated azlactone 6. Reaction of 6 with a nucleophile such as OH, OR, or NHR leads to the corresponding A-acyl-DHA derivatives 7. Reaction with the sodium salt of an amino acid gives a DHA containing dipeptide acid. 51 ... 

Plochl, in 1883, prep d the first unsaturated azlactone by the condensation of benzaldehyde with hippuric acid in the presence of acetic anhydride. However, it remained for Erlenmeyer to determine the structure of the product, to extend the reaction to other aldehydes... 

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