Enantioselective synthesis of γ- and δ-lactones

Reductive Cyclizations of Hydroxysulfinyl Ketones: Enantioselective Access to Tetrahydropyran and Tetrahydrofuran Derivatives

“…Reduction of β-ketosulfoxides 5 and 6 with DIBALH in the presence of ZnBr 2 afforded β-hydroxysulfoxides [R,-(S)R]-7 (67% yield) and [R,(S)R]-9 13 (87% yield) with an excellent diastereoselectivity (de >98%). In the reaction of compound 5, a byproduct characterized as 3-[(ptolylsulfinyl)methyl]cyclopentanone (8) 14 was isolated in 13% yield. When DIBALH alone was used to reduce the ketosulfinyl ester 6, compound [S,(S)R]-10 was exclusively formed.…”

Saturated and unsaturated lactones

“…Enantiomerically pure b-lactones are synthesised by a highly st ereoselect ive chelat ion-con trolled reduction of homochiral sulfinyl 0x0 acids (Scheme 59). 63 The addition of zinc bromide is required for satisfactory control over the reduction of the keto acids 84. One drawback at present is the inseparable mixture of substituted keto acids 84 (R # H) produced in the initial stages of the synthesis.…”