The propargyl Claisen rearrangement is a known protocol to gain access to functionalized allenes through the [3,3]-sigmatropic transformation of propargyl vinyl ethers. The correct use of appropriate propargyl vinyl ethers as starting materials coupled with suitable reaction conditions can aid in the development of new domino methodologies in which the allenes are valuable intermediates in route to a wide range of important classes of organic compounds.

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Propargyl Claisen rearrangement: allene synthesis and beyond

2, 6-Dimethylphenyl propargyl ether (10) and its derivatives 12–15 rearrange thermally to 1, 5-dimethyl-6-methylene-tricyclo [3.2.1.02,7]oct-3-en-8-one (9) and related compounds 16–19. The ethers undergo first an aromatic [3, 3]-sigmatropic rearrangement to ortho-allenyldienones 11, which then undergo ring closure to the tricyclic products by an electrocyclic reaction.



Only in the case of the γ-methylpropargyl ether 13, the ortho-dienone 11 is further rearranged in low yield to the para-butynylphenol 20, but the tricyclic ketone 17 is again the main product.



New data show that the known thermal cyclisation of aryl propargyl ethers to chromenes (e. g. 4 8) involves a preliminary [3, 3]-sigmatropic rearrangement.

Sigmatropische Umlagerungen von Aryl‐propargyläthern; Synthese von 1, 5‐Dimethyl‐6‐methylen‐tricyclo[3, 2, 1, 02,7]‐oct‐3‐en‐8‐on‐Derivaten. Vorläufige Mitteilung

Publisher Summary This chapter discusses the synthetic routes, physical properties, and reactions of indolizines. One of the synthetic routes presented is Tschitschibabin reaction involving the quaternization of a 2-substituted pyridine, normally using an α -halo carbonyl compound, followed by intramolecular cyclization of the quaternary salt with a mild base, usually aqueous sodium bicarbonate. Another route is ring closure reactions providing indolizines unsubstituted in the five-membered ring. Several physical properties including electronic spectra, acid–base properties, mass spectra, infrared spectra, nuclear magnetic resonance (NMR) spectra and X-ray diffraction are described. The most widely investigated reaction of the indolizine nucleus is electrophilic substitution. The other reactions of indolizines discussed are cyclizations, reduction, oxidation, and polymerization. Cyclization is concerned with reactions that result in the fusion of one or more additional rings to the indolizine system. Various indolizines containing vinyl groups in the pyridine ring are synthesized by polymerization reactions.

Advances in Indolizine Chemistry

Synthesis, stereochemistry, structural classification, and chemical reactivity of natural pterocarpans.

The aza-annulation of β-enamino ester and amide substrates with the mixed anhydride of 2-acetamidoacrylic acid was used for the efficient construction of highly substituted α-acetamido δ-lactam products. With the α-acetamido substituent, lactam functionality, and γ-carboxylate group, these δ-lactam products represent an interesting class of conformationally restricted dipeptide analogs. The framework of this lactam hub is structurally related to that of an α-amino acid coupled with a β-amino acid. When α-amino esters derived from naturally occurring amino acids were used in the enamine formation step, subsequent aza-annulation led to branched peptide surrogates with two C-termini that extended from a common N-terminus. Oxidation of the aza-annulation products resulted in the generation of a planar system with peptide functionality radiating from the 1, 3, and 5 positions of the pyridone hub. Alternatively, pyridone products could be formed directly from the enamino amides by reaction with 2-phenyl-4-(etho...

Formation of Dihydropyridone- and Pyridone-Based Peptide Analogs through Aza-Annulation of β-Enamino Ester and Amide Substrates with α-Amido Acrylate Derivatives

B.S. Thyagarajan

Papers

Studies in claisen rearrangement—II

Studies on quinolizones—I : Nitration of 4H-quinolizin-4-one

Studies in claisen rearrangement - I, 2-butyn-1,4-diyl bis-(aryl ethers)

Studies on quinolizones—II: Bromination and acetylation of 4H-quinolizin-4-ONE

Studies on quinolizones—III