Action of diazomethane on (Z/E)-2-methyl(or phenyl)-4-benzylidene-5(4H)-oxazolones

Abstract

We have been interested in the synthesis of (Z/E)-2methyl(or phenyl)-4-(a-arylethylidene)-5(4fl)-oxazolones 5 and 6 for several years. Although earlier authors1 found that acetophenones and hippuric acid could not condense under Plóchl-Erlenmeyer conditions, 2-phenyl derivatives were prepared2 with moderate or low yields in acetic anhydride and lead acetate as isomeric mixtures with the Z isomer predominating. The pure isomers were obtained by crystallization or by suitable isomerization procedures. Attempts to prepare 2-methyl derivatives have been unsuccessful. On the other hand several workers3 have inti) Rao, Y. S.

Elusive Dehydroalanine Derivatives with Enhanced Reactivity

“…Addition of diazomethane to freshly generated 2 directly yielded the spirocyclic cyclopropane 4 in 10 min. The common pyrazoline intermediate, ring contraction of which through N 2 extrusion normally requires thermal or photochemical activation, such as with analogous ( Z / E )‐4‐benzylidene‐2‐phenyloxazol‐5(4 H )‐ones, was not observed. Compound 4 could be fully characterised by X‐ray diffraction of monocrystals (Figure S6).…”

Natural Occurrence, Syntheses, and Applications of Cyclopropyl-Group-Containing α-Amino Acids. 1. 1-Aminocyclopropanecarboxylic Acid and Other 2,3-Methanoamino Acids

“…Starting in 1937 with the discovery that oxazolinone-protected 2-(5-methoxycarbonyl-2,4-dimethylpyrrol-3-yl)aminoacrylic acid and the (1-acetylindol-2-yl)-substituted analogue upon exposure to diazomethane furnished the correspondingly 2-substituted oxazolinone-protected 1-aminocyclopropanecarboxylic acids 158 (Table , entries 1 and 2), several other 2-hetaryl-substituted spirocyclopropanated oxazolinones ( E )- and ( Z )- 158 (R 1 = heteroaryl), and from them the corresponding 2-substituted 1-aminocyclopropanecarboxylic acids 160 have been prepared (entries 3−6). ,, Since then, especially aryl-substituted compounds ( E )- and ( Z )- 158 (R 1 = aryl) have been investigated (entries 8−50), − but also methyl- (entries 51−53), , halo- (entries 54−58), − acyloxy- (entries 59 and 60), and organothio-substituted (entries 61−64) spirocyclopropanated oxazolinones ( E )- and ( Z )- 158 have been synthesized. Starting from only one diastereomer of 156 , the stereochemical information is often lost during the cyclopropanation sequence; however, under certain reaction conditions, diastereomerically pure cyclopropanation products could be obtained in moderate yields (Table ).…”