Abstract Tris(pentafluorophenyl)boron is an efficient, air stable, and water tolerant Lewis acid catalyst for the aldol-type and Michael reactions of silyl enol ethers with carbonyl compounds or other electrophiles (trimethyl orthoformate, dimethyl acetal, and chloromethyl methyl ether), the allylation reaction of allylsilanes with aldehydes, and the Diels–Alder reaction of dienes with α,β-unsaturated aldehydes. A solution of formaldehyde in water is applicable as an electrophile. Also, the aldol-type reaction of ketene silyl acetals with aromatic or aliphatic imines is successfully carried out using the same catalyst.