Co-host: The Chemical Society of Japan, The Society of Synthetic Organic Chemistry, Japan (Cooperation)
In the present study, stereoselectivities were examined in the PD-tethered reaction of the diazo compound synthesized from (R,R)-2,4-pentanediol and catechol in four steps. When the rhodium catalyst was added to a CDCl3 solution of the diazo ketoester at room temperture, cyclic ether products were obtained in a 76% yield. The diastereomer excess (de) of the intramolecular O-H insertion was 84% at highest. Kinetic protonation of the enolate generated from the product gave the product mixture of isomer ratio up to 30:70. This kinetically protonated product was isomerized with acetic acid and DABCO to give the thermodynamic mixture, which is similar to that obtained by the O-H insertion reaction. That is, the stereoselectivity of the O-H insertion is close to that controlled thermodynamically. However, it was confirmed that the isomerization of the product did not occur under the reaction condition. The stereoselectivity must be controlled at the later stage of the reaction.
