The Aldol Reaction of Allenolates with Aldehydes in the Presence of Magnesium Diiodide (MgI₂) as Catalyst

Stereoselective synthesis of (Z)-α-(hydroxyalkyl)-β -iodoacrylates (=(2Z)-2-(hydroxyalkyl)-3-iodoprop-2-enoates) was achieved in a one-pot coupling reaction from methyl prop-2-ynoate, Me₃SiI, and an alkanal under mild conditions with MgI₂ as catalyst (→ 1-9; see Table and Scheme 1). Baylis-Hillman β-iodo adducts were generated in excellent yields with high (Z)-selectivity. The conversion of methyl prop-2-ynoate to an active methyl 3-iodo-1-[(trimethylsilyl)oxy]allenolate intermediate in situ followed by carbonyl addition is proposed as the reaction sequence (Schemes 1 and 2).