Mechanistic Investigations of the Pd‐Catalyzed Hydrogenolysis of Ketene Heterodimer β‐Lactones

Catalytic hydrogenolysis of the Z ‐isomer of a series of aryl‐substituted ketene heterodimer β‐lactones facilitated access to deoxypropionate derivatives with a dr ranging from 54:46 to 86:14, favoring the anti ‐isomer, and with excellent transfer of chirality (91 → 99 % ee for 13 examples). Although X = 4‐F was determined to provide optimal diastereoselectivity ( dr 86:14), a non‐linear relationship between diastereoselectivity and aryl substituent σ values was found. For cases where a para ‐ or ortho ‐EWG was present on the aryl ring of the ketene heterodimer, formation of significant amounts of β‐lactone (20–44 %) as by‐product was observed. The results of a number of control reactions point to anti ‐β‐elimination and an anti ‐selective hydrogenation of an E ‐isomer olefin intermediate being key steps in the reaction mechanism. The synthetic potential of the deoxypropionate derivative products was demonstrated by oxidative conversion into a 1,5‐difunctionalized deoxypropionate motif.