Zur Chemie der Cycl[4.3.2]azine

Flitsch, Wilhelm; Gurke, Annelie; Müter, Bernhard

doi:10.1002/cber.19751080918

Cited by 26 publications

(3 citation statements)

References 13 publications

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“…Figure 4) but not all compounds prove the existence of coherent peripheral ring currents. Only one of this category of cyclazines, N[2.3.4], has been synthesized by Flitsch et al [76] A peripheral paratropic ring current of N[2.3.4] was assumed due to the high-field δ( 1 H)/ppm values and to be strongest along the seven-membered ring moiety; planarity of N[2.3.4] was concluded from the vicinal H,H-coupling constants. [76,77] The TSNMRSs of N[2.3.4] (cf.…”

Section: Cyclazines Containing One 7-membered Ring Moietymentioning

confidence: 99%

“…Only one of this category of cyclazines, N[2.3.4], has been synthesized by Flitsch et al [76] A peripheral paratropic ring current of N[2.3.4] was assumed due to the high-field δ( 1 H)/ppm values and to be strongest along the seven-membered ring moiety; planarity of N[2.3.4] was concluded from the vicinal H,H-coupling constants. [76,77] The TSNMRSs of N[2.3.4] (cf. Figure 4) confirm these findings: (i) The ring system proves planar but the peripheral ring current does not exist.…”

Section: Cyclazines Containing One 7-membered Ring Moietymentioning

confidence: 99%

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Cyclazines‐Structure and Aromaticity or Antiaromaticity on the Magnetic Criterion

Kleinpeter

Koch

2022

Eur J Org Chem

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Structure and spatial magnetic properties, through‐space NMR shieldings (TSNMRSs), of all ten cycl[2.2.2]azine to cycl[4.4.4]azine, hetero‐analogues and the corresponding hydrocarbons have been calculated at the B3LYP/6‐311G(d,p) theory level using the GIAO perturbation method and employing the nucleus independent chemical shift (NICS) concept. The TSNMRS values (actually, the ring current effect as measurable in 1H NMR spectroscopy) are visualized as iso‐chemical‐shielding surfaces (ICSS) of various size and direction, and employed to readily qualify and quantify the degree of (anti)aromaticity. Results are confirmed by NMR [δ(1H)/ppm, δ(15N)/ppm] and geometry (planar, twisted, bow‐shaped) data. The cyclazines N[2.2.2]− up to N[2.4.4]− are planar or at most slightly bowl‐shaped and, due to coherent peripheral ring currents (except in N[2.3.3]−, N[2.3.4], N[3.3.4]+ and N[2.4.4]+), develop aromaticity or anti‐aromaticity of the whole molecules dependent on the number of peripheral conjugated π electrons. The cyclazines N[2.3.3]−, N[2.3.4], N[3.3.4]+ and N[2.4.4]+ develop two ring currents of different direction within the same molecule, in which the dominating ring current proves to be paratropic (in N[3.3.4]+ diatropic) including the nodal N pz lone pair into the conjugation. The residual cyclazines N[3.4.4], N[4.4.4]− and N[4.4.4]+ are heavily twisted and, therefore, are not developing peripheral or diverse ring currents. The TSNMRS information about cyclazines and the parent tricyclic annulene analogues is congruent subject to structure and number of peripheral or internal conjugated π electrons, the corresponding (anti)aromaticity is in unequivocal accordance with Hückel's rule.

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Section: Cyclazines Containing One 7-membered Ring Moietymentioning

confidence: 99%

Section: Cyclazines Containing One 7-membered Ring Moietymentioning

confidence: 99%

Cyclazines‐Structure and Aromaticity or Antiaromaticity on the Magnetic Criterion

Kleinpeter

Koch

2022

Eur J Org Chem

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“…Speci cally, when the medium ring is involved, the di culty in synthesis might be further increased due to its high torsional strain, unfavorable entropic and enthalpic factors, [13][14][15][16][17][18] and other reasons. Previous routes for synthesizing NCPC start from α-formyl-pyrrole [19][20][21][22] or -pyridine 23 as raw materials involved a cumbersome multi-step strategy, and the related methods were also extremely rare (Fig. 1c).…”

Section: Introductionmentioning

confidence: 99%

Divergently Access N-center 5,6,7-Perifused Cycle

Han

Yue

et al. 2023

Preprint

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Nitrogen-containing heterocycles are the key components in many pharmaceuticals and functional materials. In this study, we reported a transition metal-catalyzed high-order reaction sequence for synthesizing a structurally unique N-center 5,6,7-perifused cycle (NCPC). The key characteristics included the formation of a seven-membered ring by the 8π electrocyclization of various alkenes and aromatic heterocycles as π-components, in which metal carbene species generated that further induced the cleavage of the α-C-H or -C-C bond. Specifically, the latter could react with various nucleophilic reagents containing -O, -S, -N, and -C. The stereo-controlled late-stage modification of some complicated pharmaceuticals indicated the versatility of this protocol.

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TheVilsmeier Reaction of Fully Conjugated Carbocycles and Heterocycles

Jones

Stanforth

1996

Organic Reactions

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In 1925 Fischer, Müller, and Vilsmeier published a paper describing the reaction between phosphoryl chloride and N ‐methylacetanilide, giving a number of products, including the quinolinium salt and another salt. The probable course of the reaction was given in a paper by Vilsmeier and Haack in 1927, and they made the important discovery that the reagent obtained from N ‐methylformanilide and phosphoryl chloride, represented as a salt, would react with N,N ‐dimethylaniline, giving 4‐ N,N ‐dimethylaminobenzaldehyde. No 2‐substituted products were observed in this reaction. Other N,N ‐dialkylaniline derivatives, including 3, N,N ‐trimethylaniline and 1‐ N,N ‐dimethylaminonaphthalene were also successfully used as substrates to prepare aromatic aldehyde derivatives. The gradual development of the reagent for synthesis was accompanied by interest in the nature of the reagent. It was discovered that other acid chlorides (e.g., thionyl chloride, carbonyl chloride, and oxalyl chloride) could be used in the reaction and that substituted amides other than formamides gave ketones, although in generally poorer yields. Thionyl chloride frequently gives sulfur‐containing products. The most commonly used amide is dimethylformamide (DMF) and there is now a consensus that the reagent formed from DMF and most acid chlorides, other than phosphoryl chloride, can be represented by the structure given in the chapter, and this is illustrated for the reaction between DMF and carbonyl chloride. The salt is a stable compound and is often isolated before being reacted with a substrate. It seems likely that the most commonly used reagent, that made from DMF and phosphoryl chloride, is an equilibrium mixture of iminium salts. Recent unpublished spectroscopic studies have indicated that in DMF solution there is an equilibrium mixture of iminium compounds. One of the electrophilic chloroiminium salts then reacts with a substrate in an electrophilic substitution process yielding an iminium salt, which is usually hydrolyzed to the aromatic aldehyde. Vinylogous chloroiminium salts can be prepared from the corresponding vinylogous formamide derivatives and these yield, after hydrolysis, α,β‐unsaturated products. This particular reaction is generally limited to more reactive substrates. The formation of carbon–carbon bonds to fully conjugated carbocycles and heterocycles is the subject of this chapter; a subsequent chapter considers carbon–carbon bond‐formation reactions in alkenes (including heterosubstituted alkenes such as enamines and enol ethers), alkynes, and activated methyl and methylene compounds (aldehydes, ketones, carboxylic acid derivatives, and nitriles). It is not surprising that the Vilsmeier reaction has been the subject of many review articles of varying scope and length. With so many excellent reviews dealing with the Vilsmeier reaction, its mechanism, and the structure of the various electrophilic reagents, coverage is restricted to important concepts rather than reiterate all the literature material. A brief description of the mechanism and regiochemistry of the Vilsmeier reaction is presented and this is elaborated with appropriate cases that deal with specific compound types.

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Zur Chemie der Cycl[4.3.2]azine

Abstract: Chem. Commun. 1969,24; F. Gerson, J. Joachirnowicz und D. Leaver, J. h e r . Chem. Soc. 95,6702 (1973).

Cited by 26 publications

References 13 publications

Cyclazines‐Structure and Aromaticity or Antiaromaticity on the Magnetic Criterion

Cyclazines‐Structure and Aromaticity or Antiaromaticity on the Magnetic Criterion

Divergently Access N-center 5,6,7-Perifused Cycle

TheVilsmeier Reaction of Fully Conjugated Carbocycles and Heterocycles

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