Thiamine is essential for
The  enzyme  pyruvate  dehydrogenase catalyses  (oxidative  decarboxylation)  the irreversible conversion of  pyruvate to  acetyl CoA. This reaction is dependent on thiamine pyrophosphate.
Isocitrate dehydrogenase
Succinate dehydrogenase
Pyruvate dehydrogenase
Acetyl CoA synthetase