Big Chemical Encyclopedia

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

Articles Figures Tables About

Sulfur diimide symmetrical

Several methods for the preparation of unsymmetrical sulfur diimides RN=S=NR have been developed. One approach involves the addition of a catalytic amount of an alkali metal to a mixture of two symmetrical sulfur diimides, RN=S=NR and RT8i=S=NR. A second method makes use of alkali-metal derivatives of [RNSN] anions.Eor example, derivatives in which one of the substituents is a fluoroheteroaryl group can be prepared by the reaction of the anionic nucleophile [RN=S=N] with pentafluoropyridine. Sulfur diimides of the type RN=S=NH (R = 2,4,6- Bu3C6H2S) have also been prepared. "... [Pg.186]

Protonation of the anion SN2 by acetic acid in diethyl ether produces the thermally unstable sulfur dimide S(NH)2. Tike all symmetrical sulfur diimides, the parent compound S(NH)2 can exist as three isomers (see Scheme 4). Ab initio MO calculations indicate that the (cis, cis) configuration is somewhat more stable than the (cis, trans) isomer, while the (trans, trans) isomer is expected to possess considerably higher energy. [Pg.4652]

The adducts formed in these cases are the analogous dihydrothiazine imines 2. Symmetrical and unsymmetrical sulfur diimides are available, and both can act as heterodienophiles. In adducts 1 and 2 the sulfur center is chiral, and the implications of this fact will be discussed in some of the following sections. [Pg.7]

The resulting iV-sulfinyl derivatives can often be distilled and/or crystallized but are water sensitive and thus are frequently prepared in situ for subsequent cycloaddition reactions. Symmetrically substituted sulfur diimides can usually be prepared by the reaction of SCI2 or S2CI2 with the parent NH2 compound in the presence of a base such as pyridine or triethylamine [Eq. (4)]. ... [Pg.7]

In the case of sulfur diimides. X-ray and electron scattering studies have shown that the E,Z geometry 7 or 8 is favored in the solid state. - H- and C-NMR spectroscopy at low temperatures in solution indicated two isomeric forms are present an E,Z isomer 7 or 8 and a symmetrical isomer, presumed to be the E,E isomer 6. From coalescence of the H-NMR signals at higher temperatures, it has been concluded that rapid interconversion of the ( ,Z)-7 or -8 and (E,E)-6 forms occurs. [Pg.8]

Levchenko and Balon" have examined the regiochemistry of cycloaddition of several symmetrical bis(aryl)sulfonyl sulfur diimides with ( )-piperylene and isoprene which afforded the C-3 and C-5 substituted adducts, respectively (Scheme l-III). These results were confirmed by Wucherpfennig and Kresze, who also found that chloroprene gave the 5-substituted product. ... [Pg.10]

Various types of electron-deficient sulfur diimides react as hetero-dienophiles. In general, these cycloadditions occur under conditions similar to those used for AT-sulfinyl compounds. However, fewer types of sulfur diimides have been utilized in this process relative to Af-sulfinyl compounds. Some examples of symmetrical sulfur diimide Diels-Alder reactions are listed in Table l-II. It should again be noted that the orientational selectivity in these cycloadditions is the same as that shown by N-sulfinyl systems (cf. Table l-I). Several examples of cycloadditions with unsymmetrical sulfur diimides are shown in Table l-III. In all cases, these reactions were totally regioselective, and as noted above, reactions occurred at the least electron-deficient nitrogen-sulfur bond. Frontier molecular orbital (FMO) theory has been used to rationalize the regio-selectivity of addition of the cationic sulfur diimide shown in entry... [Pg.14]

The first structural characterization of a tellurium diimide RNTe(p-N Bu)2TeNR (R = PPh2NSiMe3) was reported in 1994. Subsequently, the synthesis of the symmetric derivative, R = Bu, was achieved by the reaction of Li[HN Bu] with TeClq in a 4 1 molar ratio in toluene. Several LiCl-containing byproducts are also obtained in this solvent. In THF, however, the tellurium diimide, BuN-Te(p-N Bu)2TeN Bu, is obtained in 90% yield and is readily purified." Unlike sulfur or selenium diimides, the tellurium diimides are dimeric and form either cis or... [Pg.42]


See other pages where Sulfur diimide symmetrical is mentioned: [Pg.191]    [Pg.376]    [Pg.198]    [Pg.396]    [Pg.397]   
See also in sourсe #XX -- [ Pg.16 ]




SEARCH



Diimide

Sulfur Diimides

Sulfur diimide

© 2024 chempedia.info