Substrate-Controlled Diastereoselectivity Reversal in NHC-Catalyzed Cross-Benzoin Reactions Using N‑Boc‑N‑Bn-Protected α‑Amino Aldehydes

The effectiveness of utilizing N-Bn-N-Boc-α-amino aldehydes in cross-benzoin reactions with heteroaromatic aldehydes is demonstrated. The reaction is both chemoselective and syn-selective, making it complementary to the anti-selective cross-benzoin reaction of NHBoc-α-amino aldehydes. Good diastereoselectivity is obtained for a variety of amino aldehydes, including nonhindered ones. A Felkin–Anh model can be used to rationalize the observed diastereoselectivity.