[4 + 3] Cycloaddition of aromatic α,β-unsaturated aldehydes and ketones with epoxides: one-step approach to synthesize seven-membered oxacycles catalyzed by Lewis acid.J Org Chem. 2011 Jan 21; 76(2):669-72.JO
A novel intermolecular [4 + 3] cycloaddition method to construct 1,4-dioxide seven-membered oxacycles was developed. This one-step method was carried out in the presence of catalytic amount of (C(2)H(5))(2)OBF(3) under mild conditions. Seven-membered oxacycles and some natural compounds could be easily synthesized via this protocol. Control experiments were carried out and possible mechanism for the reaction was proposed. Asymmetric reactions were proceeded and 3e was obtained with moderate ee value.