Methyl isocyanate general reactions

Isocyanates are compounds with the general formula R-N=C=0. They have numerous uses in chemical synthesis, particularly in the manufacture of polymers with carefully tuned specialty properties. Methyl isocyanate is a raw material in the manufacture of carbaryl insecticide. Methyl isocyanate (like other isocyanates) can be synthesized by the reaction of a primary amine with phosgene in a moderately complex process, represented by reaction 15.8.1. Structures of three significant isocyanates are given in Figure 15.7. 

Vinyl ethers undergo many cycloaddition reactions similar to those which take place with enamines. In general, however, these cycloaddition reactions with vinyl ethers take place less readily than those with enamines. These reactions include cycloaddition of vinyl ethers with ketene (200-205), phenyl isocyanate (206), sulfene (207,208), methyl acrylate (209), diethyl acetylenedicarboxylate (210), and diphenylnitrilimine (183). 

Bisulfite addition products are formed from aldehydes, methyl ketones, cyclic ketones (generally seven-membered and smaller rings), a-keto esters, and isocyanates, upon treatment with sodium bisulfite. Most other ketones do not undergo the reaction, probably for steric reasons. The reaction is reversible (by treatment of the addition product with either acid or base ) and is useful for the purification of the starting compounds, since the addition products are soluble in water and many of the impurities are not. ... 

In yet another example of an in situ reductive generation of an enolate, fi-amido esters are formed via the reaction of an o, /3-unsaturated ester with a silane in the presence of an isocyanate (Eq. 294).475 The yields obtained using methyl acrylate and methyl crotonate as substrates are generally excellent. 

The insertion of various isocyanates into chromium(lll) alkoxide M—O bonds has been reported.737 The complexes are prepared by refluxing the isocyanates with a suspension of the alkoxide in benzene. No structural data were given for the products. Unusual bimetallic alkoxides have recently been prepared738 by the reaction of Cr[Al(OPr )4]3 with alcohols and acetylacetone (166). A wide range of spectroscopic methods were used to study them. In general, the results were in accord with a monomeric formulation similar to (166) below Cr[Al(OMe)4]3 was grossly insoluble the small size of the methyl groups may permit extensive polymerization. 

Transient carbene (9) is expected to be a reaction intermediate in the transformation of butadiyne-linked triazene (8) to alkyne-linked bis-2//-indazolcs (10).18 Experimental data and DFT calculations support carbene (9) as an intermediate in this stepwise, non-synchronous coarctate reaction. Methoxy(methylthio)carbene (12) has been observed by UV photoelectron spectroscopy after gas-phase decomposition of oxadiazoline (11).19 The oxadiazoline (13) allows the generation of the acetoxy(methoxy)carbene (14) 20 -pjjg reaC jvj y 0f (he latter with isocyanates has been explored. Such reactions generally yield methyl (acetylamino)oxoacetates (15). DFT calculations permitted interpretation of the experimental data. 

It is a general rule that imidazoles and benzimidazoles are resistant to Friedel-Crafts reactions. This is not surprising since such basic compounds must be markedly deactivated in the presence of Lewis acids. Imidazolin-2-ones appear to be an exception and apparently possess sufficient activation to react. Reactions between imidazoles and Af-methylfor-manilide and phosphoryl chloride are also unproductive. With 4,5-diphenylimidazole, phenyl isocyanate at 80 °C gives products of both N- and C-substitution, but in boiling nitrobenzene only the latter (86) is formed. 2-Methyl-4-phenylimidazole gives (87) under the same conditions, and 1,3-diphenylimidazolium perchlorate is transformed by potassium t-butoxide into a ylide which reacts at C-2 with phenyl isothiocyanate. Sufficient activation is present in l-methyl-2-phenyl-4-phenylaminoimidazole for it to react by substitution at C-5 with acetic anhydride (71JOC3368). 

Another more general approach to enamides derived from an acetylphosphonate is based on 1,2-dichloroethyl isocyanate. This compound underwent Arbuzov reaction with methyl phosphorodichloridite to yield the 2-chloroethyl compound which, when treated... 

There are other amine surrogates that can be used to prepare amino acids by reaction with halides or other electrophilic species. Most are rather specific, but one shows some generality. Effenberger showed that reaction of methyl 5-bromohexan-oate 1.19) with potassium isocyanate gave 1.81. In this case, the isocyanate is the amine surrogate, and hydrolysis with concentrated HCl at 100°C gave 6-amino-hexanoic acid, 1.82, as its HCl salt. 4-Aminobutanoic acid, 3-aminopropanoic acid and 5-aminopentanoic acid were prepared in an identical manner.47... 

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