Precursor azides, production

Another attractive method for E ring formation featured an intramolecular [2+3]cycloaddition of an azide moiety, emanating from the indole 3-position via a two-carbon linker, to, now, an electron-rich version of the C15-C16 double bond.19 The cycloaddition precursor 10 was made via 9, in turn assembled by regioselective cocylization of protected methoxyacetylene (Scheme 5). In a puzzling turn of events, thermolysis of the azide product in toluene at moderate temperature (to minimize nitrene formation) and in low concentration (to suppress intermolecular reactions) produced the two oxidized pentacyclic products 11 and 12 in a 2 1 ratio. Performing the reaction in a more polar solvent (DMF, 80 °C, 7 d) altered the ratio to 5 1.20... 

Figure 18.5 MALDI-TOF mass spectra of the precursors and product for the construction of a tricyclic paddle-shaped polymer topology, (a) Cyclic prepolymer having an alkyne functionality (b) Three-armed star prepolymer having azide termini (c) Tricyclic paddle-shaped product.

Precursor Azides, Technical Production and Properties 2.2.1 Sodium azide (NaNs)... 

Sodium azide is the most frequently used precursor azide for both, laboratory scale and technical production. In commercial production, it is obtained in two ways ... 

When unacylated azides are used as nitrene precursors, the first reaction with an alkene is a cydoaddition, generating the corresponding 1,2,3-triazoline, which often eliminates N2 under the fierce reaction conditions to give an aziridine product (Scheme 4.9 ). 

Treatment of 51 with an excess of sodium benzoate in DMF resulted in substitution and elimination, to yield the cyclohexene derivative (228, 36%). The yield was low, but 228 was later shown to be a useful compound for synthesis of carba-oligosaccharides. <9-Deacylation of228 and successive benzylidenation and acetylation gave the alkene 229, which was oxidized with a peroxy acid to give a single epoxide (230) in 60% yield. Treatment of 230 with sodium azide and ammonium chloride in aqueous 2-methoxyeth-anol gave the azide (231,55%) as the major product this was converted into a hydroxyvalidamine derivative in the usual manner. On the other hand, an elimination reaction of the methanesulfonate of 231 with DBU in toluene gave the protected precursor (232, 87%) of 203. 

Aziridines are important compounds due to their versatility as synthetic intermediates. In addition, aziridine rings are present in innumerable natural products and biologically active compounds. Nitrene addition to alkenes is one of the most well established methods for the synthesis of aziridines. Photolysis or thermolysis of azides are good ways to generate nitrenes. Nitrenes can also be prepared in situ from iodosobenzene diacetate and sulfonamides or the ethoxycarbonylnitrene from the A-sulfonyloxy precursor. 

Fig. 5.2 Top Photochemical production of Fe(V) from a ferric-azide precursor. Bottom Mossbauer spectra observed for the precursor (green) and the photoproduct (red)...

The Fe(lll)-azide-precursor and the photolysed product were characterized by NIS spectroscopy coupled to detailed DFT calculations [63]. The result of the study provides additional evidence in favor of a low-spin 5=1/2 ground state of the Fe(V)-nitrido complex. Here we show how first-principles calculations assist in quantitative analysis of experimental NIS data for the Fe(lll)-azide complex. 

Acyl azides (see Section 2.13) The acyl-azide method of coupling is unique for two reasons. First, it is the only case in which the immediate precursor of the activated form of the peptide is not the parent acid. The starting material is the peptide ester that is obtained from the amino acid ester by usual chain assembly (Figure 2.25, path A). Second, it is the only method that just about guarantees production of a peptide that is enantiomerically pure, provided scrupulous attention is paid to details of procedure. There is no danger for loss of chirality during conversion of the ester to the hydrazide and then the azide, but care must be taken to avoid contact of... 

Differential triflate reactivities as just described similarly gave access to the regioisomeric tricunines 6 and from a single precursor, the unsymmetrical diazido sugar 89 (Figure 14). Action of sodium azide upon the diepoxide (readily prepared from had been known known to give mainly the symmetrical counterpart 88 (35), but was now found (53) to yield additionally the (partial) anti-FUrst — Plattner product, on a practical scale. Sequential displacements in its ditriflate, with azide followed by benzoate and in reverse order, furnished 2,3,3 - and 2,3,2 -triazido D-manno.D-manno derivatives, respectively, which were used to prepare 65 and by standard manipulations. The tetraamine was synthesized via double displacement, with azide, from the ditriflate of 88 (53). 

The introduction of two [5,6]-aza bridges shows a remarkable regioselectivity even if segregated alkylazides are used [17]. The diazabishomofullerenes 23 (Scheme 10.3) are by far the major products and only traces of one other bisadduct with unidentified structure are found if, for example, a twofold excess of azide is allowed to react with CgQ at elevated temperatures [17]. To obtain clues on the mechanism of this most regioselective bisadduct formation process in fullerene chemistry a concentrated solution of an azahomofullerene precursor 24 was treated with an alkyl azide at room temperature. 

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