Studies on the Chemistry of Heterocyclics. XXII. Investigations on the Mechanism of Reactions of 2-Thienyl Halides with Sodium Amide and Sodium Acetylide in Liquid Ammonia

Vaitiekunas, Alexander; Nord, F. F.

doi:10.1021/ja01103a537

Cited by 38 publications

(25 citation statements)

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“…Sharma and co-workers have reported an efficient synthesis of tri/tetrasubstituted imidazoles, including the imidazole glycoconjugates, using ZrCl 4 as an acid catalyst under neutral reaction conditions at room temperature (Scheme 43) [96]. The condensation of 1,2-diarylethanedienones (108) with aldehydes or aldehydes and amines in the presence of an excess of NH 4 OAc resulted in 2,4,5-trisubstituted and 1,2,4,5-tetrasubstituted imidazoles (109) respectively in the presence of 20 mol% of ZrCl 4 . Terepthaldehyde with 2 equiv of benzil and excess of NH 4 OAc gave bis imidazolyl benzene in 84% yield.…”

Section: Synthesis Of Tri-and Tetrasubstituted Imidazolesmentioning

confidence: 99%

“…Halogen migration on aromatic substrates in the presence of a strong base, also known as the 'halogen dance', was discovered in the 1950s [109,110]. Recently, it has been reported that ZrCl 4 is capable of smoothly promoting halogen migration during an electrophilic amination of halogenated phenols (Scheme 54) [112].…”

Section: The Migration Of Halogen On Aromatic Substratesmentioning

confidence: 99%

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Applications of Zirconium (IV) Compounds in Organic Synthesis

Zhang¹,

2009

COC

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Section: Synthesis Of Tri-and Tetrasubstituted Imidazolesmentioning

confidence: 99%

Section: The Migration Of Halogen On Aromatic Substratesmentioning

confidence: 99%

Applications of Zirconium (IV) Compounds in Organic Synthesis

Zhang¹,

2009

COC

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“…The method can be used for the preparation of various ethynylthiophenes under mild conditions [38]. Similarly, phenylacetylene is produced from a-chlorostyrene [39], and 1,3,5-triethynylbenzene (12) can be obtained in 60 % yield from ( l l ) , which does not react with boiling methanolic potassium hydroxide [40].…”

Section: E L I M I N a T I O N By A L K A L I M E T A L A M I D E Smentioning

confidence: 99%

“…An alternative mechanism could involve elimination of hydrogen halide to yield phenylpropiolic acid (38), which decarboxylates extremely readily [9]. Dehydrobromination of ~-broino-rruns-cinnamic acid (39) by aqueous alkali does in fact occur even below 20 "C [70].…”

Section: )mentioning

confidence: 99%

Eliminations from Olefins

Köbrich

1965

Angew. Chem. Int. Ed. Engl.

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increase in the rate of reaction with increasing dielectric constant of the solvent found in the acid-catalysed hydrolysis of esters [1,221. VI. Concluding RemarksDiscussion of the importance of the mobility of protons in the course of chemical reactions has been attempted in this paper, using acid-catalysed esterification as an example. Conditions are considered which are significant, not only in esterification, but in proton-catdlysed [22] K. J. Laidler and P. A. Lnndskroener, Trans. Faraday SOC. 52, 200 (1956).reactions generally. Our observations are necessarily incomplete and have the character of an approximation. However, we believe that the great importance of protons in chemistry justifies our attempted interpretation.We wish to thank Prof. G. Scheibe for his helpful interest in this work. We are also indebted to thz Deutsche Forschungsgemeinschaft, the Fonds der Chemischen Indw strie, and the Badische Anilin-und Sodafabrik for financially and materially supporting our investigations on "Protonic States in Chemistry".Eliminatiotts from olefiny are very ofren initiated by bases, and usually lead to formation of acetylene derivatives. In view of the numerous side-reactions and subsequent additions or rearrangements observed, the nature of the base used is of considerable significance. Organometallic bases are very versatile. In addition to dehydrohalogenation, dehalogenation by metals, and also thermolytic and photolytic eliminations (e.g. the retrodiene reaction with exchange of substituents) are discussed. Elimination from low-membered cyclic olefins yields cycloalkynes having strained ring-systems, and the exis fence of these can be denioiistrated by trapping them. The mechanisms known for @-elimination ( E 2 , E l and ElcB) occur also in the case of olefins; howeverdue to the sp2-hybridization of the carbon atoms taking partthey are realized with diflerent rates of reaction relative to saturated corm pounds. a-Eliminations from olefines having aryl residues in the @-position lead to formation of arylacetylenes by rearrangement of the carbon skeleton. The mechanism of this reaction, which is known as the Fritsch-Buttenberg-Wiechell rearrangement, is discussed in considerable detail, and several variations of the reaction are considered. According to presentday knowledge carbenes are involved in r-eliminations only when both @-positions of the olefin are occupied by aliphatic substituents, or when they are occupied by aromatic residues where rearrangement to acetylenes is impossible for steric reasons (as for example with 9-chlorornethylenefuorene) . With organolithium compounds a number of dehydrohalogenations, which are formally @-eliminations, actually proceed via deprotonation on the halogenbearing carbon atcm (u-metallation). a-Metallations are the rate-determining steps when ether is used as solvent, but proceed quickly in tetrahydrofuran even at low iemperatures. Compounds of the type >C=C(Li)CI may be prepared by this method and are recognized as intermediates in u-eliminations.

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“…The halogen dance reaction was first reported in 1953 4 and was intensively applied over the following years on aromatic and heteroaromatic systems such as thiophene, 5 benzo[b]thiophene, 6 furan, 7 isothiazole, 8 imidazole, 9 pyrazole, 10 pyridine, 11 quinoline, 12 and very recently, on thiazole. 13…”

mentioning

confidence: 99%