Heteroaromatic compounds reactions with carbenes

Heteroaromatic compounds, reactions with carbenes 82KGS723. 

Few examples of the preparation of six-membered heteroaromatic compounds using Fischer-type carbene complexes have been reported [224,251,381]. One intriguing pyridine synthesis, reported by de Meijere, is sketched in Figure 2.35. In this sequence a (2-aminovinyl)carbene complex first rearranges to yield a complexed 1 -azadiene, which undergoes intermolecular Diels-Alder reaction with phenylacetylene. Elimination of ethanol from the initially formed adduct leads to the final pyridine. 

Among the known classes of heteroaromatic carbenes, the benzimidazole derivatives have received the least attention thus far. They [89] present new results in terms of the synthesis and properties of stable heteroaromatic monocarbenes and biscarbenes of the benzimidazole series. One of the major aims in this area was the attachment of sterically bulky groups to the benzimidazole nucleus. The introduction of the 1-adamantyl substituent into the benzimidazole system was achieved by direct adamantylation of benzimidazole using 1-bromoadamantane in the presence of sodium acetate in acetic acid. However, in this case the reaction was incomplete and yields of only 33% of pure salt 134 were realized. In o-dichlorobenzene in the presence of potassium carbonate, a 54% yield of l-(l-adamantyl)benzimidazole (86) can be achieved and this compound can be further quatemized by treatment with 1 -bromoadamantane in o-dichlorobenzene to afford a high yield of salt 134 (90%).As is well known, in the... 

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