the Deuterium oxide step seems to be irreversibly, yielding another titanium oxide Tebbe and the side product. Therefore each molecule that reacts is lost, may the reaction be as unfavoured as it is. also the five membered ring constrain may shift equilibrium of the intermediate step towards metallacycle. maybe less side product with cyclohexanone?

if you activate your tebbe reagent with base you may be better on not doing so, since the overreaction demands another coordination to the metal. this may be less favoured when your tebbe reagent is still in its trimethylaluminium stabilized form. it is unknown to me if the Tebbe reagent is then reactive enough for the demanded firstvreaction.

the Deuterium oxide step seems to be irreversibly, yielding another titanium oxide Tebbe and the side product. Therefore each molecule that reacts is lost, may the reaction be as unfavoured as it is. also the five membered ring constrain may shift equilibrium of the intermediate step towards metallacycle. maybe less side product with cyclohexanone?

if you activate your tebbe reagent with base you may be better on not doing so, since the overreaction demands another coordination to the metal. this may be less favoured when your tebbe reagent is still in its trimethylaluminium stabilized form. it is unknown to me if the Tebbe reagent is then reactive enough for the demanded first reaction.