Rearrangements isonitriles

Isocyanates132 react with appropriate azide salts to yield 1-substituted tetrazoline-5-ones (68) (Eq. 13). By contrast, isothiocyanatesi33,i34 react with hydrazoic acid to yield the aminothiatriazole (69) which rearranges to the thione (70) under mild alkaline conditions (Scheme 8). Ugi and co-worker126,127 found that when the reaction of isonitriles and hydrazoic... 

Isonitrile insertion into zirconacycles to afford iminoacyl complexes 28 is fast, but rearrangement to q2-imine complexes 30 is slow. In the case of tBuNC, the rearrangement does not occur. Amines 32 are formed on protonolysis of the q2-imine complex. The q2-imine complexes 30 readily undergo insertion of Ti-components (alkenes, alkynes, ketones, aldehydes, imines, isocyanates) to provide a wide variety of products 37 via zirconacycles 36. The overall sequence gives a nice demonstration of how a number of compo-... 

Isomorphic monomers, 19 762 Isoniazid, 25 798 Isonicotinic hydrazide, 21 103 Isonitrile complexes, platinum, 19 656 Isonitrile-nitrile rearrangement, 21 149 Isononanoic acid, physical properties, 5 35t Isononyl alcohol, properties of commercial, 2 12t... 

The acidity of the propargylic proton of the starting compound 18 allows the equilibration with the allene 19 induced by bases such as tertiary amines or alcoholates (Scheme 7.4). Such prototropic rearrangements furnish the title compounds 19 with at least one proton at the terminal carbon atom, often in good yields. The EWG group involves carboxylic acids [33], esters [34], ketones [35, 36], isonitriles [37], sul-fones [38], sulfoxides [39, 40] and phosphonates [41], The oxidation of easily accessi-... 

An interesting route to 98 was suggested by Cramer et al. " cyclization of isonitrile 110 could lead to 98 in a rearrangement analogous to the Bergman cyclization. The activation enthalpy for the only slightly exothermic reaction was estimated at 18 kcal/mol. However, this novel access to m-arynes could not be realized experimentally so far. 

The rearrangement of methyl isonitrile (CH3NC) to acetonitrile (CH3CN) is a first-order reaction and has a rate constant of 5.11 X 10-5 s 1 at 472 K. 

Unusual triethylamine-catalysed rearrangements of bicyclic endoperoxides derived from substituted cycloheptatrienes have produced383 a variety of products (see, e.g., Scheme 80). Ab initio calculations have shown that energised 2,3-epoxypropoxide anions undergo a degenerate Payne rearrangement in the gas phase via a three-centre mechanism.384 It has been reported385 that treatment of isonitrile epoxides (330) with... 

According to Scheme 4 elimination of a proton from the iminodiazonium ion (I) forms the nitrile. Rearrangement of the ion (I) leads to formanilide. But there are no data available supporting these ideas. Another possible way for the formation of nitrile is a rearrangement of the iminocarbonium ion (II) of the type which occurs in the isomerization of isonitriles to nitriles". It was found that in 71.2-90.4% sulphuric acid, phenyl isocyanate is converted quantitatively into formanilide. For a better understanding of the... 

Carbenes add to cyclooctyne (14) to give the corresponding cyclopropenes or compounds, which can be considered as rearrangement products of these cyclopropenes 214). The addition of isonitriles is typical for seven membered cycloalkynes 8,215) the rate of formation of the cyclopropenimines depends on the electrophilicity of the isonitriles 215). Electron deficient isonitriles, such as p-nitrophenylisonitrile, add much faster than alkylisonitriles. 

In addition to these common types of reactions, several syntheses are known in which HFA causes changes in the substrate (e.g., isomerization of nitriles to isonitriles) or rearrangements of initially unstable products. However, only few exceptions to the above-mentioned examples have been found so far in HFA chemistry. 

With excess HFA a dioxolaneimine 99a is formed from a typical isonitrile reaction mentioned in previous sections. Acidification yields the unsubstituted five-membered ring 99, which is the parent compound of alkylated dioxolanes 99b-e available from isonitriles (R = Me, Et, t-Bu, c-CgHu) 111, 188). Whether the imine structure 99 or the ketone structure 101 has to be assigned to the hydrolysis product is not known. The Chapman rearrangement has been proved in the following system [Eq. (86)] 190). Treatment of 98 with strong bases like l,8-diazabicyclo[5.4.0]undec-7-ene (DBU) yields a spirocyclic compound 100 with elimination of HCN the structure of 100 has been derived by spectroscopic methods 193). The reaction of 98 with HFA X HjO (91) in sulfuric acid produces a l,3-dioxolan-(4)one 112). 

The reaction mechanism most likely involves an initial condensation of the amino functionality of the a-amino acid 168 with the aldehyde 169 to form iminium ion 171. After a-addition, intermediate 172 is formed which is attacked by the solvent methanol, to form derivative 174 after rearrangement. This compound stiU has a free carboxylic acid, which can undergo a P-3CR in the same pot to afford 175. The drawback of this procedure is that two equivalents of the aldehyde and isonitrile inputs are used, which also limits the substituent variability. 

Obviously the formation of a strong silicon-oxygen bond is also assumed to be the driving force in these rearrangements. In the presence of isonitriles, no silyl shift could be induced in complexes 3 and 4. 

Insertion of isonitriles into zirconacycles affords )] -iminoacyl complexes that smoothly rearrange to stable f-irame zirconocenes. In the case of 2-phosphanozirconaindenes, rearrangement proceeds leading to -imine zirconocenes (Scheme 35). Subsequent formation of a /3-phosphano indenoimine is obtained by elimination of Cp2Zr fragment for the 2,6-dimethylphenyl isocyanide." ... 

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