Substituent-Controlled Regiodivergent Rearrangement of Gramine Ammonium Ylide

The complicated mechanism makes the regiodivergent rearrangement of ammonium ylide seem to be out of reach. Herein, we reported a regiodivergent rearrangement of gramine ammonium ylide well controlled by the substituents. Density functional theory studies reveal that the ammonium ylide with a more steric hindrance substituent 2-diazo-2-arylacetate goes through a stepwise mechanism to yield both a kinetically and thermodynamically preferred [1,2]-rearrangement product. In contrast, the ammonium ylide with a less steric hindrance ethyl diazoacetate goes through a concerted mechanism to generate the [2,3]-rearrangement product, which is kinetically favored as a result of the release of the ring strain in the transition state. This study would open up avenues to grasp the rearrangement of ammonium ylide, which will promote application in the skeletal editing and synthesis of complex natural products.