Michael Addition-Lactonization of Arylacetyl Phosphonate to β,γ-Unsaturated α-Keto Esters for the Synthesis of Chiral syn-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).