The Aminopropenal‐ and Aminopentadienal Rearrangement

Abstract

Scope and mechanism of the aminopropenal rearrangement are reviewed: Various 3‐acyloxy‐3‐dialkylaminopropenals (2, formed by addition of acids to ‘push‐pull’‐acetylenes 1) rearranged quantitatively to give 3‐acyloxyacrylic amides (3, Schemes 1 and 22). Since these activated enol esters reacted very selectively with amino groups of polyfunctional amino acids, ‘push‐pull’‐acetylenes are versatile peptide reagents. Similarly, 5‐X‐5‐dialkylaminopentadienals (38, formed by addition of acids to ‘push‐pull’‐enynes 37) could be rearranged (aminopentadienal rearrangement). In this case, the rearrangement 38→40→42 (Schemes 16 and 22) normally stopped at the level of the quite stable 2‐dialkylamino‐pyrylium salts 40. Ring opening 40→42 of these intermediates was quite tricky, but could be realized in several cases.