Isocyanate rearrangement

We entered this field when we studied the photoisomerization of simply substituted nitrile oxides 138 (R = Cl, Br, CN).188 Matrix irradiation yields the corresponding isocyanates 144. In the case of chloronitrile oxide besides the absorptions of chloroisocyanate189 the bands of chloronitrene190 also appear. It can be assumed that the nitrile oxide-isocyanate rearrangement starts with the ring closure 138 - 140.191192... 

An account has appeared166 of [3,3]-(and [2,3]-)sigmatropic rearrangements of propargyl precursors that lead to the synthesis of allenes bearing functional groups with at least two heteroatoms (see Scheme 36). The allyl cyanate to isocyanate rearrangement has been established as a new synthetic method for the construction... 

Y. Ichikawa, M. Osada, I. I. Ohtani, and M. Isobe, A new synthetic method for the preparation of amino sugars through an allyl cyanate-to-isocyanate rearrangement, J. Chem. Soc., Perkin Trans. 1, (1997) 1449-1455. 

The acyl azide - isocyanate rearrangement is known to proceed stereospecifically with retention of both optical and geometrical (cis-tranSy endo-exo) configuration. Thus, optically active aminocyclopropanes were obtained from optically active cyclopropane carboxylic acid derivatives A lot of exo-amiobicyclo[n.l.O]alkanes or... 

Banert, K., Melzer, A. The first direct observation of an allylic [3,3] sigmatropic cyanate-isocyanate rearrangement. Tetrahedron Lett. 2001, 42,6133-6135. 

The IR spectra of the copolymers had strong absorption bands at 1710 cm"1 (pyrrolidone unit) and 1580 cm"1 (aminimide carbonyl). When films of the copolymers were heated (150°-200°C), the band at 1580 cm-1 vanished and a new strong band appeared at 2250 cm"1 which was indicative of the described aminimide-isocyanate rearrangement. Again, the NMR spectra had poor resolution but the broad bands indicated DHA and NVP moieties. 

Synthesis of nitrogen-containing natural products using allyl cyanate-to-isocyanate rearrangement 06Y96. 

A synthesis of the marine diterpene geranyllinaloisocyanide 1652 has been successfully accomplished by a novel regioselective allylamine construction, which is achieved by an allyl cyanate-to-isocyanate rearrangement 1649 —> 1650. The resulting formamide 1651 is dehydrated with triphenylphosphane/tetrabromomethane to give the geranyllinaloisocyanide 1652 in 82% yield [1226]. 

A [3,3]-sigmatropic cyanate-isocyanate rearrangement has been identified as a route to a-isocyanato allylboronic esters that can be trapped with nucleophiles (Scheme 2). A DFT (density functional theory) investigation of [3,3]-sigmatropic rearrangement versus a [2 4-2]-cycloaddition of a formal 5 2 substitution of imido metal complexes with allylic electrophiles has been reported (Scheme 3). ... 

Ichikawa and co-workers have published a number of papers disclosing an allyl cyanate to isocyanate rearrangement and its application to the synthesis of aminosugars [44,45]. A nitrogen substituent can be introduced into the pyra-... 

The intermediates in making amines are isocyanates (0==C==N) just like the Hofmann Rearrangement. The isocyanates are decomposed with water, just like the Hofmann. In fact, there is a lot of similarity between the Hofmann and the Schmidt reactions. Before I detail the synthesis steps, I should note that if you wish to generate the Hydrazoic Acid in the flask by adding Sodium Azide, you might need a powder addition funnel. This bit of equipment is quite pricey and it s likely you won t have one, so the first part of the synthesis details how to make the Hydrazoic Acid separately. 

Acyl azides may loose N2 on heating and rearrange to isocyanates (Curtius rearrangement), which may be solvolyzed. Some of the possibilities of classical carboxyl conversions are exemplified in the schemes below, which are taken from a triquinacene synthesis (R. Russo, 1971 C. Merder, 1973) and the ergotamine synthesis of A. Hofmann (1963). 

The preparation and properties of these tertiary aminimides, as weU as suggested uses as adhesives (qv), antistatic agents (qv), photographic products, surface coatings, and pharmaceuticals, have been reviewed (76). Thermolysis of aminimides causes N—N bond mpture foUowed by a Curtius rearrangement of the transient nitrene (17) intermediate to the corresponding isocyanate ... 

Preparation from Nitrene Intermediates. A convenient, small-scale method for the conversion of carboxyhc acid derivatives into isocyanates involves electron sextet rearrangements, such as the ones described by Hofmann and Curtius (12). For example, treatment of ben2amide [55-21-0] with halogens leads to an A/-haloamide (2) which, in the presence of base, forms a nitrene intermediate (3). The nitrene intermediate undergoes rapid rearrangement to yield an isocyanate. Ureas can also be formed in the process if water is present (18,19). 

Rearrangement involving cleavage of the C—O bond is also observed with the phenyl isocyanate adduct (59). In place of an O-acylated nitrone its product (60) of acyl migration is isolated (67JPR(36)86). 

Irradiation of the A-bromo- or N- chloro-azetidin-2-ones (71) in the presence of alkenes, alkynes or radical donors induces rearrangement to the /3-haloalkyl isocyanates (72) via a... 

A third approach to 3-amino-/3-lactams is by Curtius rearrangement of the corresponding acyl azides. These are readily prepared from r-butyl carbazides, available via photochemical ring contraction of 3-diazopyrrolidine-2,4-diones in the presence of f-butyl carbazate (c/. Section 5.09.3.3.2). Thus treatment of (201) with trifluoroacetic acid followed by diazotiz-ation gives the acyl azide (202) which, in thermolysis in benzene and subsequent interception of the resulting isocyanate with r-butanol, yields the protected 3-amino-/3-lactam (203) (73JCS(P1)2907). 

Rearrangement of 0-acyi hydroxarrac acxl derivatives with base or heat to amines or urea derivatives (via isocyanates) or rearrangement of carboxylic acids via their hydroxamic acxis to amines... 

The third approaeh to synthetic polymers is of somewhat less commereial importance. There is in fact no universally accepted deseription for the route but the terms rearrangement polymerisation and polyaddition are commonly used. In many respects this process is intermediate between addition and condensation polymerisations. As with the former teehnique there is no moleeule split out but the kinetics are akin to the latter. A typical example is the preparation of polyurethanes by interaction of diols (di-alcohols, glycols) with di-isocyanates Figure 2.7). 

The thermal decomposition of an acyl azide 1 to yield an isocyanate 2 by loss of N., is called the Curtius reaction - or Curtius rearrangement. It is closely... 

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