Catalytic acyloin-type heterocoupling of thioesters via a putative cobalt siloxycarbene

α-Oxy-metallocarbenes exemplify Fischer carbenes and find use in the synthesis of diverse materials. Most, however, arise from the addition of reactive organometallics to toxic metal carbonyls. Here we report a method to access α-siloxycarbenes from thioesters via the reductive silylation of cobalt acyls. The reaction results in carbonyl dimerization with high hetero- and stereo-selectivity to yield unsymmetrical tetrasubstituted disiloxyalkenes, while avoiding competitive decarbonylation. These products can be further elaborated to new functionalized fragments, heterocycles and challenging enolsilanes. Several different reactivity patterns combined with mechanistic interrogation converge on α-oxycarbenes as fleeting catalytic intermediates, indicating a way to generate and exploit these reactive species under mild conditions. This method provides a general platform to harness carbene reactivity from carboxylates via metal acyls and enables a range of diverse reactivities.