Imidoyl isocyanates

From Imidoyl Isocyanates, Imidoyl Isothiocyanates, or Imidoylcarbodiimides... 

A -Aryl-A -(ethoxyearbonyl)iinidamides and 2-alkyl-l-aryl-3-(ethoxycarbonyl)isothioureas 12 cyclize thermally to yield 2-substituted quinazolin-4(3//)-ones 13. When an A-aryl-A -(ethoxy-carbonyl)imidamide is boiled briefly in quinoline, ethanol is evolved and the corresponding 2-arylquinazolin-4(3//)-one is formed in 49-88% yield. Presumably elimination of ethanol yields an imidoyl isocyanate which undergoes cyclization to form the 2-arylquinazolin-4(3//)-one. These cyclizations are most likely simple thermal processes, since they proceed equally well when diphenyl ether is used instead of quinoline or when the imidamide is heated at 50-70 C above its melting point in the absence of a solvent.This reaction is also suitable for the synthesis of benzo-fused quinazolin-4(3//)-ones. °... 

The incorporation of the 1,3-diaza-1,3-butadiene system into a reactive heterocumulene system, imidoyl isothiocyanates and imidoyl isocyanates [Eq. (54)],l30 137... 

The reaction of isocyanates with suitable substrates also afford [3+2] and [4+2] cycloadducts. In [4+2] cycloaddition reactions the isocyanates usually participate as dienophiles. However, acyl-, thioacyl- and imidoyl isocyanates often participate as dienes in [4+2] cycloaddition reactions. In this manner numerous heterocyclic five- or six-membered ring compounds, respectively, are obtained. The 1,4-dipolar substrates can also be generated in situ using suitable catalysts. 

The reaction of phenyl isocyanate with t-butyl-A-(2,6-dimethylphenyl)imidoyl isocyanate proceeds similarly. A double [4+2] cycloaddition occurs in the reaction of carbonyl diisocyanate with aliphatic isocyanates to give l,3,5-triazino[2,l-b]-l,3,5-oxadiazine tetrones 471. ... 

Also, the relatively unstable imidoyl isocyanates undergo self-condensation (R = Ph) to give 479 or undergo cyclodimerization to give 480 . ... 

Trialkylsilyl radicals add to alkyl isocyanate to form imidoyl radicals 56 (Reaction 5.38). Detailed EPR studies established intermediates 56 to be strongly bent at the carbon bearing the unpaired electron [76], The absolute rate constant for the reaction of Et3Si radical with ieri-butyl isocyanate was found to be 5.5 x 10 s at 27 °C [13], whereas the relative rate of the addition of MesSi radicals to alkyl isocyanates was found to decrease in the... 

Carbodiimides are a unique class of reactive organic compounds having the heterocumu-lene structure R—N=C=N—R. They can be formally considered to be the diimides of carbon dioxide or the anhydrides of 1,3-substituted ureas, and they are closely related to the monoimides of carbon dioxide, the isocyanates. The substituent R can be alkyl, aryl, acyl, aroyl, imidoyl or sulfonyl, but nitrogen, silicon, phosphorous and metal substituted carbodiimides are also known. The unsubstituted carbodiimide HN=C=NH is isomeric with cyanamide, H2NCN. Mono substituted carbodiimides, generated in the thermolysis of 1-substituted tetrazoles, can be isolated at liquid nitrogen temperature but isomerize to the cyanamides at higher temperatures. ... 

In the reaction of the iminophosphorane 24 with phenyl isocyanate the generated imidoyl-carbodiimide 25 undergoes cyclization to give the tricyclic compound 26. ... 

A-Phenylimidoyl isocyanates and JV-phenylbenzimidoyl isothiocyanates 8 which are easily available from the corresponding imidoyl chlorides and potassium cyanate or potassi-... 

Cycloaddition of a,3-unsaturated ketones, acyl ketenes, acyl, thioacyl, imidoyl and vinyl isocyanates, as well as the corresponding isothiocyanates, to the C=C bond of vinylidenephosphoranes leads to the formation of six-membered heterocycles carrying an exocyclic ylide function e.g. equation 117). In some instances the mentioned thioisocyanates, however, may undergo [2 + 2] cycloaddition at the C=S bond. Interestingly N-aryliminovinylidenetriphenylphosphoranes dimerize in a [4 2] cycloaddition on heating alone. 

Nitriles react with phosgene only in the presence of hydrogen chloride, to give either 1,2-unsaturated isocyanates or N-heterocyclic derivatives. The reactions are really those between COClj and the imidoyl chlorides or 1-chloroenamines, since these are the materials formed, reversibly, as equilibrium mixtures when hydrogen chloride adds to nitriles [2229] ... 

EtCN and PrCN gave the pyrimidine derivatives as major products, and PhCHjCHjCN gave the isocyanate as the major product when the quantity of benzene solvent was increased. Isocyanates may be considered to be produced via the formation of the imidoyl chloride and subsequent reaction to give the corresponding (V-carbamoyl chloride, followed by the loss of hydrogen chloride. 

The N -substituted N-imines can be prepared by the reaction of the N-aminoazonium salts, in the presence or absence of base, with anhydrides or acyl halides,8,13-17,20,21,45,46 diketene,47 diethyl malonate,48 sulfonyl chloride,8,15,49,50 /i-halovinyl ketones and esters,51-54 diethyl ethoxymeth-ylenemalonate and related compounds,53,55-57 isocyanates,17,58 thioiso-cyanates,17,58 imidoyl chlorides and imidates,59,60 nitro acetate,8,61 and active halobenzenes.62,63 Some representative pyridine -(substituted imines) prepared in this way are shown in Scheme 1. 

Cyclic derivatives have also been prepared from quinoxaline-2,3-dithiones by reaction with phosgene (COClj), thiophosgene (CSCI2), and thionyl chloride (SOCI2). 2,3-Disubstituted quinoxalines result from the reaction of the dithiones with isocyanates, isothiocyanates, and imidoyl chlorides (e.g., PhCCl=NMe). Derivatives of quinoxaline-2,3-dithiones incorporating arsenic, antimony, and tin have been prepared for example, with BujSnCl the 2,3-disubstituted quinoxaline 22 is obtained, and... 

Another interesting application of iminium chlorides in organic synthesis involves their use as catalysts in the conversion of carboxylic acids to carboxylic acid chlorides ( ), carbamates to isocyanates ( ), amino-acids to isocyanato acid chlorides and arylamine hydrochlorides to isocyanates In these reactions chlorodimethylformiminium chloride is being used, because it is readily available. However, other imidoyl halides could react in a like manner. 

The substituents in I and II are generally alkyl and aryl groups. However, recently imidoyl chlorides having N-carbethoxy and N-cyano groups have been synthesized. Dichlorination of aliphatic isocyanates in the a-position yields N-chlorocarbonyl-substituted imidoyl chlorides, and C-cyano-substituted imidoyl chlorides were found to be intermediates in the 1,2-rearrangement of N-nitrosoamides, using phosphorus pentachloride. 

In addition to azomethines and oximes, various heterocumulenes, such as ketenimines, isocyanates and isothiocyanates, can be used to synthesize imidoyl chlorides. For example, addition of chlorine to ketenimines LXIX affords a-chloroimidoyl chlorides LXX... 

The dichlorination of aliphatic isocyanates LXXI affords a,a-dichloro-alkyl isocyanates LXXII, which are predominantly in the tautomeric imidoyl chloride form LXXIII, as evidenced by infrared studies... 

By analogy with the general synthesis of imidoyl chlorides it can be expected that carbamates and thiocarbamates undergo reaction with a variety of acid halides to afford 1-haloformimidates and 1-halothio-formimidates, respectively. For example, carbamates have been reacted with carbonyl chloride ( ), pyrocatecholphosphorus trichloride ( ), and phosphorus pentachloride ( ), and isocyanates were obtained. In view of the catalytic effect of N,N-dimethylformamide in the phosgenation of carbamates to isocyanates, the intermediacy of 1-chloroformimidates X is anticipated ( ). 

Substituted (indol-2-yl)-ct-allenols show divergent patterns of reactivity under metal catalysis and an intramolecular 1,3-iodine migration has been reported (Scheme 208). Computational methods have addressed rearrangements of acyl, thioacyl, and imidoyl (thio)cyanates to iso(thio)cyanates, acyl iso(thio)cyanates to (thio)acyl isocyanates, and imidoyl iso(thio)cyanates to (thio)acyl carbodiimides, RCX-YCN RCX-NCY RCY-NCX RCY-XCN (X and Y = O, S, NR ). ... 

Tris(TMS)phosphine can undergo a related reaction with isocyanates to furnish carbamoylphosphines and their imidate tautomers in a ratio of 9 1. Such compounds are used in the synthesis of 1,2,4-azadiphospholes and 1,3-azaphos-phinines (eq 11). Reaction with imidoyl chlorides can give 2-phosphaallylic cations,which can be condensed with hydroxylamine to give 1,2,4-oxazaphospholes and 1,2,4-diazaphospholes. " Selected examples are given in eq 12. 

When the isocyanate contains a carbonyl, thiocarbonyl or an imidoyl group adjacent to the cumulative system, a different type of dimer is formed, resulting from addition of the cumulative C=N bond to the heterodiene system in the a-substituted isocyanate to form... 

The cyclodimerization of isocyanates attached to an a-carbonyl, a-thiocarbonyl or a-imidoyl group proceeds via a [4+2] cycloaddition sequence. For example, treatment of phenylcarbonyl isocyanate with a catalytic amount of triehtylamine at 50 °C gives rise to the formation of the cyclodimer 469" . 

Imidoyl -, thiocarbamoyl - and ethylmercaptothiocarbonyl isothiocyanatesalso afford dimers formed in a [4-1-2]] cycloaddition reaction. Carbamoyl isothiocyanates are in equilibrium with thiocarbamoyl isocyanates therefore on standing mixed dimers 3 of the... 

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