NHC‐Catalyzed 1,4‐Elimination in the Dearomative Activation of 3‐Furaldehydes towards (4+2)‐Cycloadditions

Abstract A dearomative formal (4+2)‐cycloaddition reaction between 2‐substituted 3‐furaldehydes derivatives and isatins or α,α,α‐trifluoroacetophenones as electrophiles has been established under NHC‐catalysis. This approach utilizes the process of hydrogen chloride 1,4‐elimination leading to a highly reactive NHC‐bound heterocyclic o ‐QDM intermediates derived from 3‐furaldehydes, which play a key role in the process. By using this strategy, a series of structurally diverse 6,7‐dihydro‐4 H ‐furo[3,2‐ c ]pyran‐4‐ones was prepared in 41–85% yields. In addition, the potential of the obtained (4+2)‐cycloadducts has been confirmed in the synthesis of interesting class of spirooxindole derivative containing 6,7‐dihydro‐4 H ‐furo[3,2‐ c ]pyran scaffold. magnified image