Exploiting Biocatalysed Processes for Telescoped Curtius Rearrangement Reactions in Flow Mode

The Curtius rearrangement of carboxylic acids i in the presence of benzyl alcohol was performed as a continuous flow process, enabling a safer and easier scale-up process. Inline purification processes, involving immobilized CALB and a mixture of A-15/A-21, were exploited to afford clean Cbz-carbamate product ii. An excess of benzyl alcohol was required to drive the reaction to completion. Therefore, immobilized CALB was employed to chemoselectively transform the residual benzyl alcohol into easily separable benzyl butyrate iv. To demonstrate the versatility of the products, the Cbz-carbamate ii was further derivatized into alkylated Cbz-carbamate v and ß- amino acids vi.