The Baylis-Hillman reaction is quite different from acylations. In this case, DMAP adds in Michael reaction fashion to cyclohexanone to form the intermediate (1) below that is stabilized in dipolar form. The activated enolate (green) is attacked by electrophiles (formaldehyde) to afford hydroxymethyl cyclohexanone¹.

Figure 1

 DABCO (1,4-diazabicyclo[2.2.2]octane) has often been the catalyst of choice for the Baylis-Hilman reaction. However, when DABCO was used as the intended catalyst only starting materials were returned.¹ Another striking contrast was found between the behavior of DMAP and DABCO as catalysts in the reaction of arylaldehydes and methylvinylketone².  A diadduct was observed in this reaction when DABCO was used, however use of DMAP completely suppressed this unwanted byproduct.

Ar = p-NO₂C₆H₄

These clear differences in behavior between DMAP and DABCO tempts one to suggest that a wide study of the use of DMAP in the Baylis-Hillman reaction might prove fruitful.

1. Rezgui, F. and El Gaied, M. M. Tetrahedron Lett. 1998, 39, 5965.
2. Shi, M.; Li, C.-Q.; and Jiang, J.-K. Chem. Commun. 2001, 833.