Synthetic studies on strictamine: unexpected oxidation of tertiary amine in Ru-catalyzed ring-closing olefin metathesis

During synthetic studies toward strictamine, unexpected oxidation of tertiary amine to enamine was observed in ring-closing olefin metathesis (RCM) using Hoveyda-Grubbs 2nd catalyst. Control experiments under deoxygenated conditions indicated Ru-catalyst and electron deficient 1,4-benzoquinone additive promoted oxidation. The desired RCM reaction took place selectively under microwave irradiation by suppression of oxidation of amine.