Efficient access to aliphatic esters by photocatalyzed alkoxycarbonylation of alkenes with alkyloxalyl chlorides

Abstract

Aliphatic esters are essential constituents of biologically active compounds and versatile chemical intermediates for the synthesis of drugs. However, their preparation from readily available olefins remains challenging. Here, we report a strategy to access aliphatic esters from olefins through a photocatalyzed alkoxycarbonylation reaction. Alkyloxalyl chlorides, generated in situ from the corresponding alcohols and oxalyl chloride, are engaged as alkoxycarbonyl radical fragments under photoredox catalysis. This transformation tolerates a broad scope of electron-rich and electron-deficient olefins and provides the corresponding β-chloro esters in good yields. Additionally, a formal β-selective alkene alkoxycarbonylation is developed. Moreover, a variety of oxindole-3-acetates and furoindolines are prepared in good to excellent yields. A more concise formal synthesis of (±)-physovenine is accomplished as well. With these strategies, a wide range of natural-product-derived olefins and alkyloxalyl chlorides are also successfully employed.

Efficient access to β-amino acid ester/β-amino ketone derivatives via photocatalytic radical alkoxycabonylimidation/carbonylimidation of alkenes

“…At this stage, the excited triplet state bifunctional reagent underwent concerted fragmentation through the homolysis of the N–O bond to generate the iminyl radical and the alkoxycarbonyl/acylcarbonyloxy radical with the release of CO 2 . Furthermore, the longer lifetime of the N-centered iminyl radical 6–14 and the shorter lifetime of the acyl radical 20 have been demonstrated by previous studies. Hence, the transient alkoxycarbonyl/carbonyl radical is captured by the alkene to generate a stabilized C-centered radical at a rate approaching diffusion.…”

Stereoretentive cross-coupling of chiral amino acid chlorides and hydrocarbons through mechanistically controlled Ni/Ir photoredox catalysis

“…Here, an upfield shift of the 2a resonances and a downfield shift of the 2,6-lutidine methyl peak was witnessed. This observation is in good agreement with the analogous lutidinium salt generated from ethyl chlorooxoacetate and 2,6-lutidine, reported by the Wu group 46 . In addition, pronounced peak broadening and even separation of the α-carbonyl proton resonance were detected, likely due to the steric bulkiness of the 2,6-lutidine moiety leading to the formation of rotameric species.…”

“…However, the reduction barriers of acid chlorides (e.g., benzoyl chloride 2z , E o = −1.53 V vs SCE) are too high for these compounds to be reduced by Ir[dF(CF 3 )ppy] 2 (dtbbpy)PF 6 ( E o red = −1.37 V vs SCE), the optimized photocatalyst for reported C–H acylation reactions 42 , 43 . To solve the problem, more electron-deficient N-acylpyridinium compounds 44 , 45 , which can be formed by reacting acid chlorides with pyridine derivatives, were applied 46 .…”

Recent advances in difunctionalization of alkenes using pyridinium salts as radical precursors

“…Taking advantage of in situ formed pyridinium salts with 2,6lutidine and alkyloxalyl chlorides, Wu and co-workers reported photocatalyzed alkoxycarbonylchlorination of alkenes (Scheme 6). 13 The photocatalyst showed great effects on the reaction revealing that Ru(bpy) 3 Cl 2 was the best choice for activated alkenes, while Ir(ppy) 3 was the best one for unactivated alkenes. This transformation tolerated various electronrich and electron-deficient alkenes and provided the corresponding b-chloro esters in satisfactory yields (7a-7f).…”