Addition to isocyanates

It was found that the 15-membered macrocyclic complexes were significantly less acidic. Similar reversible protonations have been shown to occur in related macrocyclic complexes36 37 and this work has been developed by Busch into a major study of ligand reactions,38 which are summarized in equations (16)—(19). It is significant that these reactions include not only typical substitution reactions such as acylation and nitration (equations 16 and 19), but also nucleophilic addition to isocyanates (equation 17) and to a, 3-unsaturated esters (equation 18). 

The deacylated Jager-type complexes (62) can be reacylated with a variety of groups and also undergo nitration and addition to isocyanates and a,p unsaturated esters (Scheme 23).139,140... 

The azabicyclononane system is a common structural feature in diterpene alkaloids, and the nitrene insertion route to the ring system has been studied in detail in model decalins as well as in steroids (Scheme 11). Thus irradiation of the rrans-acyl azide (21) gave, in addition to isocyanate (30-33%), a mixture of Ae 7- and 8-lactams (22) and (23). The y-lactam (22) predominated, dthough the overall yield was poor. > The corresponding c/s-azide (24), however, gave the 8-lactam (25) as Ae major product, again in low yield. One elegant application of this type of intramolecular nitrene insertion reaction... 

In addition to isocyanates secondary carbamoyl chlorides are readily converted to carbonimidoyl dichlorides by high-temperature chlorination, provided one of the alkyl substituents is a methyl group (31.49-52,54 ... 

The addition to isocyanates forms the basis of a commercial route to polyurethanes, catalysed by organotin alkoxides. 

In a similar fashion, alcohols undergo addition to isocyanates (R-N=C=0), which are nitrogen analogues of carbenes, to produce esters of carbamic acids (called urethanes). Thus, as shown in Table 8.6 (item 19) and in Scheme 8.59, the addition of cyclohexanol (CeHnOH) to phenylisocyanate (C6H5N=C=0) produces the cyclohexyl ester of phenylcarbamic acid. Interestingly, as shown in Scheme 8.59, it appears that the proton found on the nitrogen of the urethane is transferred directly to nitrogen from an alcohol dimer (or trimer). 

The other potential isomer of HOCN (in addition to isocyanic acid [H-N=C=0] and cyanic acid [H-O-CfeN]) is fulminic acid (H-0-N sC ), which is also incapable of isolation as the free acid (since attempts to do so result in polymerization). However, salts of fulminic acid are known and mercury fulminate, prepared by treatment of a mixture of mercury and ethanol with nitric add, is used commercially as a detonator (blasting cap) for explosives. 

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