A mild protocol for allylation and highly diastereoselective syn or anti crotylation of aldehydes in biphasic and aqueous media utilizing potassium allyl- and crotyltrifluoroborates.

[formula: see text] Potassium allyl- and crotyltrifluoroborates undergo addition to aldehydes in biphasic media as well as water to provide the corresponding homoallylic alcohols in high yields (> or = 94%), excellent diastereoselectivity (dr > or = 98:2), and without the necessity of any subsequent purification. The presence of a phase transfer catalyst (e.g., nBu4NI) significantly accelerates the rate of reaction, whereas added fluoride ion retards the reaction.