A pedagogically useful discovery-based undergraduate organic chemistry lab experiment probing the chemoand diastereoselectivity in the NaBH 4 reduction of two chiral ketoesters (benzoin acetate and benzoin benzoate) has been developed. This experiment complements a previously described and highly popular discovery-based experiment that probes the stereoselectivity in the NaBH 4 reduction of the chiral ketone (±)-benzoin. Using reactions described in standard textbooks, students convert (±)-benzoin to the ketoester derivatives (±)-benzoin acetate and (±)-benzoin benzoate. In contrast to benzoin that has a single reducible ketone functional group, the ketoester derivatives have two reducible functional groups. In addition, the structural modifications made to the hydroxyl group of the benzoin molecule lead to an increase in the effective steric bulk of the OH group of benzoin, affording a larger acetoxy group and an even larger benzoxy group. Using NMR spectroscopy, students probe not only the chemoselectivity but also the diastereoselectivity associated with the NaBH 4 reduction of their difunctional substrates. In contrast to the NaBH 4 reduction of benzoin, which is highly diastereoselective (de ∼ 100%) and affords (R,S)-hydrobenzoin with near exclusion of its (R,R)-and (S,S)-counterparts, students discover a decreasing trend in diastereoselectivity going from benzoin to benzoin acetate and benzoin benzoate. These findings are then assessed with the help of qualitative predictions made by the Felkin-Anh model for nucleophilic addition to the carbonyl group.

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The conversion of a wide range of primary, secondary aliphatic and a few arylamine hydrochloride salts to their corresponding acetamides with trimethyl orthoacetate (TMOA) is described. Mechanistic studies using NMR and GC-MS techniques indicate these reactions proceed via an O-methylimidate intermediate that undergoes in situ demethylation by chloride affording the corresponding acetamides. Synthetically, this reaction represents a practical, high-yielding protocol with a simple workup for the rapid conversion of amine hydrochloride salts to acetamides.

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