DFT study on selective autocatalyzed α-alkylation of ketones with alcohols

Base-promoted transition-metal-free α-alkylation of ketones with alcohols is an efficient, practical, and green method for the formation of new CC bonds. Here, we present a DFT study on NaOH/KOH-promoted selective autocatalyzed α-alkylation of ketones with alcohols. For the production of alkylated alcohol, the disodium alkoxide species Na1D is the mediator, and the transformation involves four stages: (I) aldehyde formation; (II) aldol condensation; (III) chalcone reduction to generate an alkylated ketone and an aldehyde; and (IV) reduction of the alkylated ketone to produce an alkylated alcohol. Stage I only occurs at the beginning of the reaction, and the subsequent reaction proceeds via the catalytic cycle cyc-Na involving stages II, III, and IV. The energetic span and the turnover frequency (TOF) of cyc-Na are 35.2 kcal/mol and 5.7×10-7 1/s, respectively. For the production of alkylated ketone, the dipotassium alkoxide species K1D is the mediator, and the transformation includes dioxygen-assisted oxidation of alkylated alcohol (stage V) and the above four stages. Stage I only takes place initially, too, but the subsequent reaction has two selectable channels. The main channel is the catalytic cycle cyc-K consisting of stages II and III. The energetic span and the TOF of cyc-K are 29.5 kcal/mol and 8.8×10-5 1/s, respectively. The side channel involves stages II, III, IV, and V, in which the apparent activation energy (AAE) is 34.1 kcal/mol. The calculations present the TOF-determining intermediates and the TOF-determining transition state, and uncover the essence of autocatalysis and the origins of the product selectivity. One important finding is the alkylated ketone selectivity may be enhanced by adding a small quantity of aldehyde corresponding to the alcohol reactant and lowering the reaction temperature.