Dynamic resolution of 2-cyclohexylidene acetaldehydes through organocatalytic dienamine [4+2] cycloaddition†
Organocatalytic formed dienamines are shown to be involved in dynamic resolution of 2-cyclohexylidene acetaldehydes. By reaction of racemic 2-cyclohexylidene acetaldehydes with benzoquinones in the presence of a diarylprolinol-silyl ether catalyst, tricyclic products are formed in good to high yield and excellent enantioselectivity, while the diastereoselectivity depends on the substituent in the 2-cyclohexylidene acetaldehydes. Studies based on experimental observations and DFT-calculations point to a dynamic thermodynamic resolution-directed pathway. Some transformations of the optically active products are also presented.