Synthesis of Chiral γ‑Lactones by One-Pot Sequential Enantioselective Organocatalytic Michael Addition of Boronic Acids and Diastereoselective Intramolecular Passerini Reaction

The synthesis of α,γ-substituted chiral γ-lactones was quickly achieved in a one pot sequential process. The procedure involves an enantioselective organocatalysed transfer of boronic acid to 5-hydroxyfuran-2­(5<i>H</i>)-one, followed by an intramolecular diastereoselective Passerini-type reaction. The methodology was developed and optimized with <i>N</i>-Boc-indole-2-boronic acid giving access to α-indole-γ-substituted lactones in high yields and good diastereoisomeric and enantiomeric ratios. By applying the process to other boronic acids, the synthesis of structurally diversified α,γ-substituted chiral lactones was also achieved in good yields albeit with lower enantioselectivities