Synthesis of 3-Alkylcoumarins from Salicylaldehydes and α,β-Unsaturated Aldehydes Utilizing Nucleophilic Carbenes: A New Umpoled Domino Reaction. -A new domino reaction of salicylaldehydes with α,β-unsaturated aldehydes affords a series of coumarins. It represents the first example where N-heterocyclic carbene generated homoenolate equivalents are used in a direct synthesis of benzoannelated heterocycles. Although the reaction suffers from moderate yields, it tolerates a broad range of functionalities. While salicylaldehydes bearing a substituent in the 6-position such as (I) or (VIII) require an excess of the carbene precursor, derivatives without a shielding substituent react in the presence of stoichiometric amounts of DDIP. The reactions can be carried out in comparable yields under microwave conditions within a shorter time. In the case of cinnamaldehyde, by-products (XII) and (XIII) are observed, which can be isolated in a low yield in the absence of the salicylaldehyde substrate. -(TORAENG, J.; VANDERHEIDEN, S.; NIEGER, M.; BRAESE*, S.; Eur. J. Org. Chem. 2007, 6, 943-952; Inst. Org. Chem., Univ. Karlsruhe, D-76131 Karlsruhe, Germany; Eng.) -Kieslich 23-127
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