Carbene complexes isocyanate addition

Iwasawa et al. also developed a new reaction involving a three-component coupling process which affords five-membered heterocycles. This [2s+2sh-1c] cycloaddition reaction supposes the consecutive addition of an alkynyllithium derivative to a Fischer carbene complex followed by the addition of a third component which can be an aldehyde, an imine, an isocyanate, or C02 [119] (Scheme 74). 

The reactivity of metal-silylene complexes is more limited than the reactivity of carbene complexes. The cationic base-stabilized ruthenium-silylene complex in Equation 13.37 does not react with olefins or alkynes to undergo [2-1-2] addition reactions. However, a related complex did undergo [2-1-2] addition reactions with isocyanates, as shown in Equation 13.46. Other reactions of silylene complexes are distinct from those of carbene complexes or those of other conventional organometallic compounds. For example, the reaction of the silylene hydride with an acetylene generates a p-silylvinylarene complex... 

Addition of l,3-thiazolium-4-olates to (l-alkynyl)carbene tungsten complexes lb,n affords thiophene and/or pyridone complexes, 64 and 65, by extrusion of sulfur and isocyanate, respectively, from the [3+2] adduct formed initially (Scheme 21).97 [3+2] cycloaddition reactions of azomethine... 

The related cycloaddition of diynes with carbon dioxide has also been developed as an efficient entry to pyrones (Scheme 3-29). As observed with isocyanate couplings, initial reports described the use of phosphine complexes of Ni(0), " but more recent work with A-heterocyclic carbene ligands demonstrated considerably milder conditions and broader scope. " Additionally, the cycloaddition of diynes with nitriles efficiently proceeds to generate pyridine derivatives under similar conditions. ... 

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