Michael Addition–Lactonization of Arylacetyl Phosphonate to β,γ-Unsaturated α‑Keto Esters for the Synthesis of Chiral <i>syn</i>-3,4-Dihydropyranones and 5,6-Dihydropyranones

Catalytic asymmetric Michael addition–lactonization of arylacetyl phosphonates to β,γ-unsaturated α-keto esters by a chiral bifunctional thiourea–tertiary amine was established. Using the developed protocol, a range of optically pure syn-3,4-dihydropyranones were generated in good yields with good to excellent stereoselectivities (up to >20:1 dr and 99% ee). Meanwhile, when stoichiometric diisopropylethylamine and 1,8-diazabicyclo[5.4.0]­undec-7-ene were used as the base for the same reaction, a series of 5,6-dihydropyranones could be obtained in moderate to good yields (53–75% yield).