Über die Dimerisierung von N‐(Arylmethylen)dehydroalaninestern

Abstract

N‐(Arylmethylen)dehydroalaninester sind hochreaktive Verbindungen. Sie dimerisieren unter [4+2]‐Cycloaddition (Diels‐Alder‐Reaktion) zu rac‐3,4,5,6‐Tetrahydropyridin‐Derivaten 2, die unter geeigneten Bedingungen isoliert werden können. In Lösung tautomerisieren die Dimeren 2 zu Enaminen 3, die schnell intramolekular zum Bicyclus 4 reagieren. Diese 3,6‐Diazabicyclo‐[3.2.1]oct‐2‐en‐Derivate 4 werden diastereoselektiv gebildet. Ihre Struktur wurde durch Röntgenstrukturanalyse geklärt. Die bicyclischen Diaminodicarbonsäureester 4 stellen die stabilen Endprodukte der gesamten Reaktionsfolge dar.

Biomimetic Synthesis of Azole‐ and Aryl‐Peptide Alkaloids

“…Homodimerization of 36 was found to take place in Diels-Alder type fashion (37) even at low temperatures. In accordance with earlier work [43][44][45] the initial dehydropiperidine product 38 was highly prone to imine-enamine tautomerization, followed by an intramolecular aza-Mannich reaction. This unintended sequence could be suppressed using a scavenging amine (BnNH 2 ), which removed the side-chain imine and liberated the labile amino-dehydropiperidine product 39 as a 1 : 1 mixture of diastereomers (separable later in the synthesis).…”

Total Synthesis of the Thiopeptide Antibiotic Amythiamicin D

“…Scheme ). Although not commonly used as dienophiles because of their poor reactivity, dehydroalanine derivatives do participate in Diels−Alder reactions. − On the other hand, there is no precedent for simple enamides such as the phenyl substituted enamide 24c acting as a dienophile, and therefore this compound, along with the more relevant 2-thiazolyl substituted derivatives 24d − 24f , formed part of our early feasibility studies. Methyl 2-acetamidoacrylate 24a is commercially available, and its ethyl analogue 24b was prepared from the corresponding acid.…”

Electron-deficient 1- and 2-azabuta-1,3-dienes: a comprehensive survey of their synthesis and reactivity

“…136,137 The 3-alkoxycarbonyl-2-azabuta-1,3-dienes 256 were prepared via a reaction of arylimines 255, derived from serine esters, and CDI, followed by a base-induced elimination (Scheme 76). [138][139][140] The abovementioned studies revealed that the 4-unsubstituted 3-alkoxycarbonyl-2-azabuta-1,3-dienes 256 are quite unstable compounds. When left in solution for a short time at room temperature, dimerisation was observed with formation of tetrahydropyridine 257.…”

“…The stable hydrochloride salts of the cyclic and bicyclic amino acids, derived from 257 and 258, were obtained under mild conditions (Scheme 77). 140,141 2-Aza-1,3-diene 259 acted also as a Michael acceptor with the synthesis of amino acid derivatives 260 as a result. Especially when diorganocopper(I) reagents (R 2 CuLi) were used, the desired Michael addition was strongly preferred (Scheme 78).…”