A cheap metal catalyzed ring expansion/cross-coupling cascade: a new route to functionalized medium-sized and macrolactones

Abstract

An efficient alkoxyl radical-triggered ring expansion/cross-coupling cascade was developed under cheap metal catalysis. Through the metal-catalyzed radical relay strategy, a wide range of medium-sized lactones (9-11 membered) and macrolactones (12,...

Iron-catalyzed alkoxyl radical-mediated C–C bond cleavage/phosphorothiolation: a new approach to functionalized S-alkyl phosphorothioates

“…Encouraged by the above success, we set to examine the C–C bond cleavage/phosphorothiolation of hemiketal hydroperoxides 4 with HSP(O)(OEt) 2 2a (Scheme 5). Based on previous reports and our recent study, 14 we believe that ring expansion/phosphorothiolation would take place, enabling the combination of a lactone fragment with HSP(O)(OEt) 2 . Satisfactorily, a range of fascinating S -alkyl phosphorothioates bearing a medium-sized lactone or macrolactone moiety were constructed in moderate yields by adjusting the ring-sizes of substrates 4 .…”

Iron-Catalyzed Alkoxyl Radical-Induced C–C Bond Cleavage/gem-Difluoroalkylation Cascade

“…However, this strategy is mostly restricted to the construction of the five- or six-membered lactones. Recently, our group disclosed an elegant and cheap transition metal-catalyzed alkoxyl radical-induced ring-expansion strategy for divergent synthesis of functionalized medium-sized lactones and macrolactones . Therefore, we investigated the ring expansion/difluoroalkylation of hemiketal hydroperoxides 5 with difluoroenoxysilanes 2 , expecting to develop a distinct approach to fluoroalkylated lactones, particularly macrolactones.…”

“…Recently, our group disclosed an elegant and cheap transition metal-catalyzed alkoxyl radicalinduced ring-expansion strategy for divergent synthesis of functionalized medium-sized lactones and macrolactones. 16 Therefore, we investigated the ring expansion/difluoroalkylation of hemiketal hydroperoxides 5 with difluoroenoxysilanes 2, expecting to develop a distinct approach to fluoroalkylated lactones, particularly macrolactones. To our delight, the reactions proceeded successfully under iron catalysis to provide the desired difluoroalkylated medium-sized lactones (6a−6j) and marcolatones (6k−6m) in moderate to good yields (Scheme 3).…”

Modern Macrolactonization Techniques

“…The main drawback associated with this method is the inability of introducing functionality other than ketones on the carbon radical formed after the ring expansion. Guo, Duan, Houk and co-workers recognized this issue as an opportunity, 86 and combined the -scission of -alkoxy hydroperoxides, developed by Schreiber, with iron-and copper-catalyzed radical relay catalysis. 87,88 In this manner, they were able to develop four sets of conditions for introducing nitrile, azide, thiocyanate, and halides using TMSCN, TMSN 3 , NH 4 SCN, and hydrohalic acids on the ring-expanded products (Scheme 20).…”