Highly Chemoselective Baylis−Hillman and Aldol Reactions of 2H-Thiopyran-4(3H)-one Using Tertiary Amine Catalysts in Aqueous Media

For the first time, the Baylis−Hillman (BH) reaction of 2H-thiopyran-4(3H)-one is investigated, and surprisingly, the reaction of 2H-thiopyran-4(3H)-one with aldehydes in the presence of different tertiary amines shows excellent chemo- and regioselectivity in water. At room temperature, DBU affords BH adducts, but with DABCO, aldol products were obtained. In the case of DABCO, Et₃N, or DMAP, domino aldol−rearrangement reactions occurred at 45−50 °C.