Lewis Acid-Catalyzed Conjugate Addition-Cyclization Reactions of Ethenetricarboxylates with Substituted Propargyl Alcohols:Stereoselectivity in the Efficient One-Pot Synthesis of Methylenetetrahydrofurans

摘要

Oxygen-containing heterocyclic systems are important structures in organic chemistry because of then-presence in many biologically active compounds.In this work,a Lewis acid-catalyzed cyclization of ethenetricarboxylate derivatives 1 with substituted propargyl alcohols to give methylenetetrahydrofurans was investigated.Reaction of 1 and gamma-silicon-substituted propargyl alcohols 4 with ZnBr_2 at 80-110 °C led to (Z)-silicon-substituted products stereoselectively.Reaction of 1 and gamma-ester-substituted propargyl alcohol 7 in the presence of various Lewis acids gave ester-substituted methylenetetrahydrofurans stereoselectively.Interesting Lewis acid dependency on stereoselectivity for the reaction of 7 was found.Reaction of a-substituted propargyl alcohols also gave cyclized products.