Development of a New Reaction System for the Synthesis of Highly Optically Active α,γ-Substituted γ-Butyrolactones

A highly useful method for the synthesis of optically active α,γ-substituted γ-butyrolactones has been developed. The SmI2-induced reductive coupling of chiral 2-alkyl acrylates derived from isosorbide with ketones in the presence of (1S)-(−)-2,10-camphorsultam as a proton source give the chiral α,γ-substituted γ-butyrolactones in good yields and high enantiomeric purities (up to >99% ee for trans and 75% ee for cis). The reaction system has been investigated with various ketones, and it is demonstrated that this system is very effective for trans-α,γ-substituted γ-butyrolactones. Both the chiral auxiliary and the hindered proton source in this system are necessary for the observed excellent ee values of the products. The absolute configuration of the trans products is assigned on the basis of the X-ray crystal structure.