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Titanium(IV) Chloride and Quaternary Ammonium Salt Promoted Baylis−Hillman Reaction
journal contribution
posted on 2000-12-29, 00:00 authored by Min Shi, Yan-Shu FengThe Baylis−Hillman reaction of aldehydes with α,β-unsaturated ketones can be drastically affected
by the reaction temperature and Lewis bases. When the reaction was carried out at −78 °C using
catalytic amounts of quaternary ammonium salts (R4N+X-, X = Cl, Br, I) as Lewis bases, in the
presence of titanium(IV) chloride, the chlorinated aldol adduct 1 was obtained as the major product.
Quaternary ammonium bromides and iodides (R4N+X-, X = Br, I) have higher catalytic activity
than corresponding chlorides (R4N+Cl-). Quaternary ammonium fluorides (R4N+F-) do not have
activity at all. The amounts of Lewis acid and quaternary ammonium salts used affect the reaction
rate and product. A plausible reaction mechanism is proposed. If the reaction was carried out at
room temperature (about 20 °C) in the presence of titanium(IV) chloride and quaternary ammonium
salts (R4N+X-, X = Cl, Br, I), the elimination product 3, derived from 1, was formed as the major
product.