Temperature-Independent Stereoselectivity in Intramolecular Cycloaddition of Ketene Generated from Diazoester in Solution and in Vapor Phase: How Entropy Term Governs the Selectivity

Abstract

Abstract The intramolecular [2 + 2] cycloaddition between alkene and ketene linked with 2,4-pentanediol tether was performed in a wide range of temperature, −60 to +400 °C. When the ketene was generated by photolysis at the diazoester in a pentane solution, the cycloadduct obtained was of 90–98% de depending on the structure of the olefinic part as well as the structure of the tether. Notably, each substrate showed practically constant selectivity in a temperature range of −60 to +130 °C. The thermolysis in vapor phase above 250 °C also gave the same cycloadducts; the de values of the kinetic products are similar to those obtained by photolysis. The observed temperature-independent stereoselectivity should be controlled by the entropy term, which is also investigated by ab initio calculations in the framework of density functional theory.