Modular Synthesis of Functionalized Butenolides by Oxidative Furan Fragmentation

Abstract

The development of new chemical transformations to simplify the synthesis of valuable building blocks is a challenging task in organic chemistry and has been the focus of considerable research effort. Here we report a chemical transformation that enables the facile and modular synthesis of synthetically challenging yet biologically important functionalized butenolides from easily accessible furans. Specifically, Diels–Alder reactions between furans and singlet oxygen generate versatile hydroperoxide intermediates, which undergo iron(II)‐mediated radical fragmentation in the presence of Cu(OAc)2 or various radical trapping reagents to afford butenolides bearing a wide variety of appended remote functional groups, including olefins, halides, azides, and aldehydes. The practical utility of this transformation is demonstrated by easy diversification of the products by means of cross‐coupling reactions and, most importantly, by its ability to simplify the syntheses of known building blocks of eight biologically active natural products.

Dealkenylative Alkynylation Using Catalytic FeIIand Vitamin C

“…To put this idea into practice, we performed a preliminary investigation of the reaction conditions by reacting (−)-isopulegol ( 1a ) as a model alkene with various alkynyl donors in the presence of stoichiometric Fe II , as we had used previously for dealkenylative alkenylation (Table ). Among the range of structurally diverse alkynyl radicophiles that we tested, including the bromoalkyne 3 , , phenylpropiolic acid ( 4 ), the (phenylethynyl)­sulfone 5a , and the alkynyl triflone 6 , we found that the sulfone 5a performed the best, providing the desired alkyne 2aa in 76% yield and 85:15 dr (Table a, bars 1–7). A slight increase in the yield of 2aa and a lower diastereoselectivity occurred when changing the alkyne radical acceptor to (phenylethynyl)­benziodoxolone ( 7 ) under otherwise identical conditions (Table a, bars 8 and 9).…”

Synthesis and Characterization of Bimetallic Nanoclusters Stabilized by Chiral and Achiral Polyvinylpyrrolidinones. Catalytic C(sp3)–H Oxidation

“…Hence, a match-and-mismatch in stereochemical outcome is not as apparent compared with the result from 15 ; this may be because the active site, at C2 of 18 , is away from the C6-stereogenic center. Previously, oxidation of 18 was limited to chromic acid, singlet oxygen, or cytochromes P450 enzymes, and in most cases, ring-opening products were obtained. , …”

Synthesis, Reactivity and Activation Modes of Fluoroalkyl Thiosulfonates and Selenosulfonates

“…Finally, another methodology was exploited taking advantage on the 2 steps oxidation/fragmentation of furan derivatives published by Gui (Scheme 11D). [38] With a low catalyst loading, the starting furan is oxidized by singlet oxygen in methanol to the corresponding dihydrofuran bearing a peroxide group. A control fragmentation of the latter in the presence of stoichiometric amounts of iron releases the active carbon-centered radical which intercepts the fluoroalkylthiolated group leading to the expected products 36.…”