Cobryketone Derived from Vitamin B₁₂ <i>via</i> Palladium-Catalyzed Cleavage of the sp³–sp³ Carbon–Carbon Bond

Heptamethyl cobyrinate was transformed into hexamethyl 8-<i>nor</i>-cobyrinate. The crucial step involved the synthesis of new, vitamin B₁₂ derived cobryketone <i>via</i> palladium-catalyzed cleavage of the sp³–sp³ carbon–carbon bond with the liberation of the ketone. The replacement of sp³ carbon atom with sp² (CO) at the 8-position produces a bathochromic shift of all absorption bands and makes α and β bands equal as a consequence of the expansion of the existing conjugated system of double bonds