Enolate formation from cyclopropyl ketones via iodide-induced ring opening and its use for stereoselective aldol reaction

Treatment of cyclopropyl ketones with TiCl4-n-Bu4NI mixed reagent provides (Z)-titanium enolates which afford syn-α-iodethyl-β-hydroxyketones stereoselectively upon subsequent reaction with various aldehydes. The aldol adducts are cyclized into trans-acyltetrahydrofurans in good yield by active alumina. In contrast, the use of Et2AlI in place of TiCl4-n-Bu4NI provides the corresponding anti aldol adducts with high stereoselectivity. These methods can complementarily provide both syn and anti isomers of α-iodoethyl-β-hydroxyketones from cyclopropyl ketones and aldehydes.