Push-pull enamines in the synthesis of fused azaheterocycles

Silica gel and microwave-promoted synthesis of dihydropyrrolizines and tetrahydroindolizines from enaminones

“…In the course of our attempts at the syntheses of aryl-bearing indolizidine alkaloids via N-phenacyl vinylogous amides such as 11, however, we fortuitously found substituted 2,3-dihydro-1H-pyrrolizines 12 as unexpected products when intermediates 11 were exposed to acidic conditions, including treatment with acetic acid or even during chromatography on silica gel (Scheme 1) [18]. In these cyclizations the enaminone acts as an intramolecular nucleophile towards the phenacyl substituent, even though the nucleophilic character of the enamine component is expected to be suppressed by the "push-pull" effect arising from the electron-withdrawing carbonyl group [19][20][21][22][23]. The dual properties of enaminones as both nucleophiles and electrophiles have frequently been exploited in the synthesis of heterocyclic products, including pyrroles and related systems [22][23][24][25][26][27][28].…”

Enaminone, Enaminoesters, and Related Compounds in the Metal‐Free Synthesis of Pyridines and Fused Pyridines

“…Recently, several comprehensive reviews have appeared describing the preparation of many heterocyclic systems, among others of fused pyridinones …”

“…[7][8][9][10][11][12] In this context, the Suzuki reaction has a special significance. [10][11][12] An attractive alternative is a mild Negishi cross-coupling of 2heterocyclic organozinc reagents with aryl and heteroaryl chlorides, [26][27][28] which complements reactions with other 2-heteroarylorganometallic reagents. [13] Direct arylation and alkylation of nitropyridine N-oxides with Grignard reagents [14] and arylation of arenes and N-heteroarenes with diaryliodonium salts without the use of transition metal catalysts [15] have recently been reported.…”

“…[24][25][26] Recently, several comprehensive reviews have appeared describing the preparation of many heterocyclic systems, among others of fused pyridinones. [27][28][29] The intention of this minireview is to show the metal-free syntheses of pyridines and fused paridines have been developed.…”

Synthesis of 4‐Hetarylisoxazoles from Amino Acid‐Derived Halogenoximes and Push‐Pull Enamines

“…In this work, we have studied reactions of halogenoximes bearing a protected amino function (i.e. derived from amino acids) 5-9 ( Figure 2) and enamines bearing an electron-withdrawing (mostly hetaryl) substituent (the so-called "push-pull" enamines [42,43] ) 10-18 ( Figure 3) as a method for the synthesis of amines bearing 3,4disubstituted (preferably 4-hetaryl-substituted) isoxazole moiety. lowed by addition of 10-18 and subsequent stirring at room temp.…”