Tandem Chemoselective 1,2‐/1,4‐Migration of the Thio Group in Keto Thioesters: An Efficient Approach to Substituted Butenolides

Abstract

We report herein an efficient and mechanistically unique tandem chemoselective 1,2-/1,4-migrationo ft he thio group in keto thioesters that provides substituted butenolides in moderate to excellent yields.T hus, a-keto thioesters in the presence of stabilized phosphonate carbanions undergo tandem 1,2-sulfur migration;w hereas1 ,4-migration of the thio group has been achieved with the same thioest-ers after the treatment with Wittig reagents followed by BF 3 ·OEt 2 -catalyzed tandem reaction. Thec rossover experiments and the isolation of intermediates reveal as tepwise mechanism for botho ft hese transformations.Scheme 1. Commonstrategies for the 1,2-/1,4-migration of the thio group.

Elusive Thiyl Radical Migration in a Visible Light Induced Chemoselective Rearrangement of γ‐Keto Acrylate Thioesters: Synthesis of Substituted Butenolides

“…We also tried to verify the possibility of any thermal/ionic rearrangement after the photochemical ( E / Z ) isomerization of 1 which may bring the ketone in proximity to the thioester. For this, 1ca ( trans‐ 1ca : cis‐ 1ca = 1.5:1) in DMSO was heated at 40°C to 80°C for 12 h (Eq. b).…”

“…c), which indicates that the sulfur functionality is critical for the reaction to occur. To confirm whether 4a was formed via 1cc by an allylic migration of the sulfur substituent, 1cc was treated under the standard conditions (Eq. d) .…”

“…General Procedure for the Synthesis of 1 . All the γ‐keto acrylate thioesters were synthesized from the corresponding α‐keto thioesters by Wittig olefination reaction following our previous literature report …”

Solvent Dependent Divergent Reactivity of Electron‐Rich Dienones with and without Visible Light: Access to Cyclopropanated Furans and Butenolides

“…The formation of intermediate II was also supported by the observation that the reaction worked better in highly polar media. [22] Not surprisingly, an oxoester derivative instead of thioester did not undergo the anticipated cyclization under the optimized reaction conditions. We presume that singlet oxygen is generated in other aprotic solvents under the experimental conditions, which may be responsible for decomposition of the starting dienones.…”

“…The structures of the products were established by comparing their analytical data with those of known derivatives. [22] Not surprisingly, an oxoester derivative instead of thioester did not undergo the anticipated cyclization under the optimized reaction conditions. This is not unexpected as the oxoester is less reactive towards nucleophiles than a thioester [23] and the poor nucleophilicity of the oxygen atom hinders subsequent oxygen migration after intramolecular lactonization (Table 4).…”