Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Heterocycles four-membered

In methylene chloride or DMSO solution in the presence of catalytic amounts of protonic acids (81CC828,81ZOK2064) or under UV irradiation (81ZOK2064) cis isomers lb transform into a 1 1 mixture of cis and trans isomers, indicating the expected energy equivalence of la and lb. Both of these are characterized by an equal number of shortened intramolecular Te. . . H contacts, which were revealed by an X-ray study of trans isomer la (Ar=C6H5)(81TL1495) (Fig. 1). [Pg.50]

Crystal packing provides evidence of rather strong intermolecular attractive interactions between neighboring molecules that are justified by contracted Te. . . Te distances (3.63 A), whereas the sum of the Van der Waals radii is 4.40 A (60MI1). [Pg.51]


A few typical examples indicate the large variety of five-membered heterocycles, which can be synthesized efficiently by [2 + 3]-cycloadditions. [2 + 2]-Cycloadditions are useful in the synthesis of certain four-membered heterocycles (H. Ulrich, 1967), e.g. of 8-lactams (J.R. [Pg.152]

From Four-membered Heterocycles, Cephalosporins and Penicillins... [Pg.132]

Structure of Small and Large Rings Table 2 Structures of Known Four-membered Heterocyclic Compounds... [Pg.4]

Four-membered heterocycles are often puckered rather than planar (Table 4), As expected, exo- and e do-unsaturation tend to make these systems planar. [Pg.6]

Aside from C-H coupling constants (often obtained from satellites in NMR spectra) not very much information is available on the NMR spectra of small heterocycles. A recent review (B-79MI50101) devotes only seven pages to the NMR spectra of all three- and four-membered heterocyclics. [Pg.11]

Four-membered heterocycles prefer to cleave, upon ionization, into two fragments, each containing two of the ring atoms. Further cleavages commence from these initial fragments (Scheme 5). Specific details can be found as follows azetidines (B-71MS296), oxetanes... [Pg.11]

Four-membered heterocycles can be formed by the addition of isocyanides to 1,3-dipoles (80AG(E)45) and by the reaction of carbon monoxide with -haloamines, with the aid of palladium catalysis (Scheme 10) (79CC699). [Pg.36]

Four-membered heterocycles are easily formed via [2-I-2] cycloaddition reac tions [65] These cycloaddmon reactions normally represent multistep processes with dipolar or biradical intermediates The fact that heterocumulenes, like isocyanates, react with electron-deficient C=X systems is well-known [116] Via this route, (1 lactones are formed on addition of ketene derivatives to hexafluoroacetone [117, 118] The presence of a trifluoromethyl group adjacent to the C=N bond in quinoxalines, 1,4-benzoxazin-2-ones, l,2,4-triazm-5-ones, and l,2,4-tnazin-3,5-diones accelerates [2-I-2] photocycloaddition processes with ketenes and allenes [106] to yield the corresponding azetidine derivatives Starting from olefins, fluonnaied oxetanes are formed thermally and photochemically [119, 120] The reaction of 5//-l,2-azaphospholes with fluonnated ketones leads to [2-i-2j cycloadducts [121] (equation 27)... [Pg.853]

Tlie present chapter reviews the chemistry of three- and four-membered ring compounds containing an S—S bond in their ring. Dithiiranes 1,2-dithietanes and 1,2-dithietes are the compounds of this type. Although 1,3-dithietanes are four-membered heterocycles which are prepared much more easily and are seemingly more familiar, they have no S-S bond in the ring and hence are not included in this chapter. [Pg.220]

The fusion of four membered-heterocycles with two heteroatoms onto face a of the quinoline offers two isomeric combinations of the tricyclic ring system l,2-heterocyclo[2,3-a]quinoline and l,3-heterocyclo[3,2-a]quinoline. The later one of these two ring systems is the only one that examples of it namely, l,3-thiazeto[3,2-a]quinoline have been reported. Moreover, examples of those fused on faces ij or j are not known (Fig. 3). [Pg.76]

The diazaphosphane or aminoiminophosphane ligands with a NPN framework are another subclass of cyclophosphazenes. These compounds with both phosphorus in oxidation state (111) [104-110] and (V) [111-112] have been employed in the synthesis of four membered heterocycles and coordination chemistry with group 13 derivatives. Several complexes of trivalent phosphorus derivatives with both aluminum halide and alkyls are known as illustrated for 48 in Scheme 21 [113-119]. The structure determination of 48 confirms the formation of a four membered metallacycle [116, 117],... [Pg.111]

Table 10. Selected bond lengths (pm) and angles (°) of four-membered heterocycles [R2AlE(Tms)2l2 (E = P, As, Sb)... Table 10. Selected bond lengths (pm) and angles (°) of four-membered heterocycles [R2AlE(Tms)2l2 (E = P, As, Sb)...
In view of the reaction behavior of l,2 i.5-oxaphosphetanes (22), treated above, it appears fitting to reconsider the mechanism of the hydroxylion induced fragmentation of p-bromophosphinic acid 6443). It was assumed that formation of the phosphinate 65 is followed by that of the four-membered heterocycle 66, which spontaneously decomposes to benzalacetophenone and phenyldioxophosphorane the latter then adds water to give the phosphonie acid 43 ... [Pg.89]

B. Miscellaneous Reactions 1. Three- and Four-Membered Heterocycles... [Pg.256]


See other pages where Heterocycles four-membered is mentioned: [Pg.449]    [Pg.3]    [Pg.10]    [Pg.11]    [Pg.12]    [Pg.18]    [Pg.20]    [Pg.25]    [Pg.39]    [Pg.132]    [Pg.179]    [Pg.845]    [Pg.853]    [Pg.336]    [Pg.1]    [Pg.3]    [Pg.202]    [Pg.319]    [Pg.42]    [Pg.150]    [Pg.161]    [Pg.64]    [Pg.239]    [Pg.92]    [Pg.104]    [Pg.104]    [Pg.105]    [Pg.223]    [Pg.417]    [Pg.52]   
See also in sourсe #XX -- [ Pg.223 ]

See also in sourсe #XX -- [ Pg.488 ]

See also in sourсe #XX -- [ Pg.9 ]




SEARCH



Annulated Three- and Four-Membered Heterocycles

Carbenes Derived from Four-membered Heterocycles

Five-Membered Heterocycles with Four Hetero Atoms

Five-membered heterocycles with four heteroatom

Forming four-membered heterocycles

Four-membered

Four-membered Heterocycles containing a Single Nitrogen, Oxygen or Sulfur Atom

Four-membered heterocycle-derived

Four-membered heterocycle-derived carbenes

Four-membered heterocycles aromaticity

Four-membered heterocycles photochemistry

Four-membered heterocycles with one

Four-membered heterocycles with two

Four-membered heterocycles, review

Four-membered heterocyclic compounds from

Four-membered ring heterocycles

Four-membered ring heterocycles azetidine-2-ones

Four-membered ring heterocycles azetidines

Four-membered ring systems silicon and phosphorus heterocycles

Four-membered rings, heterocycle synthesis

Heterocyclic Four-Membered Rings, Stereochemistry of (Moriarty)

Heterocyclic compounds four-membered

Heterocyclic compounds four-membered ring opening

Heterocyclic compounds four-membered ring, formation

Heterocyclic compounds four-membered rings

Heterocyclic systems four-membered

Homologation of Four-Membered Heterocycles

Peri-Heterocycles with Four-Membered Heteroring

Phosphorus heterocycles four-membered rings

Phosphorus heterocycles, four-membered

Quinones with a Condensed Four-Membered Heterocyclic Ring

Ring Expansion into Four-Membered Heterocycles

Silicon heterocycles, four-membered

© 2024 chempedia.info