PIDA‐mediated Oxidative Decarboxylation of Oxamic Acids. The Role of Radical Acidity Enhancement.

Abstract

The PIDA-mediated oxidative decarboxylation of oxamic acids in the presence of alcohols is shown to afford the corresponding urethanes under thermal conditions. Computational and experimental mechanistic exploration allows to rationalize the different reactivity of PIDA as compared to related cyclic BI-OAc and highlights the importance of the enhanced acidity of the proton in the carbamoyl radical intermediate.

Synthesis of Polyurethanes Through the Oxidative Decarboxylation of Oxamic Acids: a New Gateway Toward Self-blown Foams

“…(acetoxy)benziodoxolone (Bi-OAc) or the commercially available phenyliodine diacetate (PIDA)). Conveniently, we demonstrated that the decarboxylation reaction can be either photo- [46,47] or thermo-initiated [45] under very mild conditions. In the first case, the oxidation is mediated at room temperature by a photocatalyst under visible light or near infrared light (NIR).…”

“…Very recently, we developed metal-free approaches to access isocyanates from oxamic acids. [45][46][47] The methodology is based on the use of hypervalent iodine reagents as lipophilic oxidants (e.g. (acetoxy)benziodoxolone (Bi-OAc) or the commercially available phenyliodine diacetate (PIDA)).…”

“…In a first trial, hexamethylene bis-oxamic acid 1a (HBOA, 1 eq., Table 1), obtained according to a previously reported procedure, [45] was used as a latent-isocyanate precursor. Di-hydroxy telechelic PEG-1500 2a (1 eq.)…”

“…Conveniently, oxamic acids are very stable and easy to handle precursors, which can be prepared from amines and oxalic acids derivatives using a simple and efficient procedure. [42] Furthermore, several oxamic analogs are considered as safe prodrugs in pharmaceutical a) Typical latent isocyanates in the literature [25][26][27] b) Urethane synthesis via the oxidative decarboxylation of oxamic acids [41][42][43][44][45]…”

Iron-Catalyzed Oxidative Decarboxylation of Oxamic Acids: A Safe and Efficient Photochemical Route to Urethanes

“…The oxidative decarboxylation of oxamic acids was carried out through photocatalysis, 9,11,12 but also electrochemistry 13 and more recently using hypervalent iodine reagents under thermal conditions. 14 In the search for more benign oxidative conditions, we lately found that cheap iron catalysts could efficiently convert oxamic acids into isocyanates (this work). Iron, being an abundant metal, iron complexes have been extensively studied in the field of photochemistry and photophysics.…”