Azido isocyanates rearrangement

There are several synthetic approaches that rely on a molecular rearrangement to incorporate the appropriate functionality. A classical reaction is the Curtius rearrangement,i43 in which an azido ketone rearranges to an isocyanate. Subsequent hydrolysis converts the isocyanate to an amine. This approach can be applied to the synthesis of amino acids. When 2,2,3,3-tetramethylbutanedioic acid (L249) was... 

Trifluoromethyl)quinazolin-4(3//)-one (6) is formed quantitatively from a-azido-a-phenyl-/1-trifluoroethyl isocyanate (3) via a nitrene intermediate 4 which undergoes rearrangement to a-(A -phenylimino)- 8-trifluoroethyl isocyanate (5) followed by cyclization to 6 (cf. p 58). °... 

The reversed reaction, i.e. attack of CO on the corresponding transition metal azido complex, sometimes also provides an attractive route for the synthesis of isocyanate complexes, e.g. the reaction of CO with, for example, Co(N3)(DH)2(PPh3), Rh(f/ -C5Me5)(N3)4 or Rh(N3)(cod). Kinetic studies indicate that depending on the steric requirements of the coligands either prior CO coordination followed by the intramolecular rearrangement shown in equation (20) or intramolecular attack of the coordinated azido group by CO is operative. ... 

Azides, Diazoalkanes, Diazirines, Azo-compounds, and Azines. Fluorinated alkanoyl azides have been dealt with already in other sections, mainly that concerned with isocyanates (see pp. 227,228, and 229). The azides CHFa Ns, (CFs)2C(N3) O SiMes, and (CF3)sC(Ns) O SOsO have been obtained from the reaction systems CHFsCl-NaNs-alkali-HsO-dioxan, (CF3)2CO-Me8Si N3,i and (CF3)2C(Ns) ONa-S2O5CIX (X = F or Cl), respectively. Eleven 2-azido-3,3>difluorocyclobutenes have been synthesized as indicated in Scheme 49 and converted thermally or photo-chemically into the corresponding 2,2-difluorocyclopropanes decomposition of the 1-cyano- and 1-methoxycarbonyl-cyclobutenes in the presence of electron ri( aromatics gave pyrrole derivatives. These results have been discussed in terms of the mechanistic pathways contained in Scheme SO Neber rearrangement with EtsN... 

We anticipated that a similar strategy would be applicable to the synthesis of l,3-oxazine-2,4-diones, involving the in situ formation of isocyanates by thermal Curtius rearrangement of acyl azides under the same conditions of the Wolff rearrangement. Indeed, tenperature-regulated microwave irradiation of a 1 1 mixture of a 2-diazo-1,3-diketone and an acyl azide afforded the desired l,3-oxazine-2,4-dione products 33 (Scheme 3.281. This sequence nicely illustrates the utilization of microwave activation for the selective one-pot thermal rearrangements of azido and diazo compounds. 

Other types of bonds undergo sonolysis, for instance the nitrogen-nitrogen bond of an azido group. The Curtius rearrangement of benzoyl azide is probably one of the first attempts to use sonication in an organic reaction. 3 phenyl isocyanate is... 

In what appears to be a dramatically different process, carboxylic adds that are resistant to attack by sulfuric add (H2SO4) can undergo substitution on the carbon of the carbonyl of the hydroxyl group (-OH) by the azido group (-N3) (in a process called the Schmidt reaction). While it is occasionally possible to isolate the acid azide, rearrangement to the corresponding isocyanate is common. A schematic representation in concert with available experimental data for the prcx ess of azide formation and subsequent rearrangement is shown in Scheme 9.120 for the case of benzenecarboxylic acid (benzoic acid). It is particularly important to note that in contrast to the typical formation of a tetrahedral intermediate so common for the... 

The monomeric imidazole-blocked 1,4-phenyIenediisocyanates with n-alkoxymethyl substituents were prepared from 2,5-bis(n-alkoxymethyI) terephthalic acids by chlorination with oxalyl chloride in DM Ac at 0 C[19 - 21] followed by reaction with aqueous NaN3 as shown in Scheme 1. The isolated azido products were rearranged to isocyanates in the presence of excess imidazole at 85 °C in toluene. On cooling were precipitated the DIS-IBDIs, which were thoroughly purified by recrystallization from acetone. The substituted terephthalic acids were prepared by basic hydroysis of 2,5-bis(n-alkoxymethyl)-terephthalonitriles[17 - 18]. 

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