From azides

Reactions of ionic or covalent azides with chalcogen halides or, in the case of sulfur, with the elemental chalcogen provide an alternative route to certain chalcogen-nitrogen compounds. Eor example, the reaction of sodium azide with cyclo-Sa in hexamethylphosphoric triamide is a more convenient synthesis of S7NH than the S2CI2 reaction (Section 6.2.1). Moreover, the azide route can be used for the preparation of 50% N-enriched S7NH. 

The polymer (SN)x may also be made in a two-step process using azide reagents. Thus the reaction of S2CI2 with sodium azide in 

MesSiNs yields (SN)x as a black solid. By contrast, the explosive and insoluble black compound SesNaCla, which probably contains the [SesNaCl] cation, is prepared by the treatment of SeaCla with trimethylsilyl azide in CH2CI2 (Eq. 2.13).  

Chalcogen-nitrogen cations can be generated by the reactions of homopolyatomic chalcogen cations with azides. For example, the 

The cyclocondensation of trimethylsilyl azide with a bis(sulfenyl chloride) is an efficient synthesis of dithiazolium cations (Section 11.3.5) (Eq. 2.15).  

i-PrOH, A JACS 84 485 (1962) 86 1427 (1964) Chem Pharm Bull 18 2368 (1970) 

(phase transfer) NaBH -exchange resin NaBHat cat CoBr2 NaBHa-excbange resin, Ni(OAc)2, MeOH JOC 47 4327 (1982) Syn Commun 20 293 (1990) JOC 60 4324 (1995) Syn Commun 23 3047 (1993) 

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In a related reaction the isocyanate from azide (109) cyclized with aminopyridine esters via a ureido intermediate to give (110) (80JHC733). 

BOC derivatives can be prepared directly from azides by hydrogenation in the presence of (BOC>20. 

Bartoli recently discovered that by switching from azide to p-anisidine as nucleophile, the ARO of racemic trans- 3-substituted styrene oxides could be catalyzed by the (salen)Cr-Cl complex 2 with complete regioselectivity and moderate selectivity factors (Scheme 7.36) [14]. The ability to access anti-P-amino alcohols nicely complements the existing methods for the preparation of syn-aryl isoserines and related compounds [67] by asymmetric oxidation of trans-cinnamate derivatives [68]. 

C. From Azides and Phosphorus(iii) Compounds.—Typical syntheses, which generally proceed smoothly at 20—50 °C, include... 

Durr, H., and Kober, H. Triplet States from Azides. 66, 89-114 (1976). 

Saxitoxin is a small tricyclic structure isolated from oceanic red tides it has attracted much interest for its peculiar structure and toxicity as a paralytic agent. The core structure that is related to a l-iminooctahydropyrrolo[l,2-f]-pyrimidine nucleus was prepared by rearrangement after oxidation of a double bond contained in a medium-size guanidine ring. This key intermediate in the synthesis was prepared from azide 376 with a judicious use of Mbs... 

The addition of methanol or hydrazoic acid to ethenylidenecydopentadiene 3 demonstrates that 3 behaves like an acceptor-substituted allene (Scheme 7.27) [226, 227]. More examples of nudeophilic additions to alkyl-substituted derivatives of 3 were reported by Hafner [228]. Photoelectron spectroscopy of the spirocyclic compound 165b, easily accessible from azide 164b, shows that the lone-pair orbital n(N) of the 2H-azirine nitrogen atom interacts strongly with the Jt1-orbital of the cyclo-pentadiene ring [227]. 

Macroscopic n-type materials in contact with metals normally develop a Schottky barrier (depletion layer) at the junction of the two materials, which reduces the kinetics of electron injection from semiconductor conduction band to the metal. However, when nanoparticles are significantly smaller than the depletion layer, there is no significant barrier layer within the semiconductor nanoparticle to obstruct electron transfer [62]. An accumulation layer may in fact be created, with a consequent increase in the electron transfer from the nanoparticle to the metal island [63], It is not clear if and what type of electronic barrier exists between semiconductor nanoparticles and metal islands, as well as the role played by the properties of the metal. A direct correlation between the work function of the metal and the photocatalytic activity for the generation of NH3 from azide ions has been made for metallized Ti02 systems [64]. 

PEPTIDE-BOND FORMATION FROM AZIDES OF N-ALKOXYCARBONYLAMINO ACIDS... 

FIGURE 2.13 Peptide-bond formation from azides of IV-alkoxycarbonylamino acids (see review by Meienhofer).35-36... 

From Azides and Phosphorus(m) Compounds.—The reactions of aminophosphines, and of phosphites, with trimethylsilyl azide are not as simple as might be expected, in view of the formation of significant quantities of by-products, (11) and (12), which have been identified.21... 

Ion exchange chromatography at pH 5.25 of the aqueous fractions yielded six peaks, I - VI (fig. 1). Peak V contained a mixture of amino acids (TLC with n-propanol/ammonia/water = 8 1 11 by vol.) (table 1). Therefore, the pooled fractions of V were separated at pH 3.5 (fig. 2). Three peaks were observed, the first probably representing ammonia formed from azide. The second peak (V-1) still displayed a minor impurity on TLC, whereas the third peak (V-2) appeared as a single spot. Peak V-1 could not be separated further by ion exchange chromatography at pH 7.0 (peak V-1-1). 

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