Photocatalyzed Generation of Nitrosocarbonyl Intermediates Under Solar Light Irradiation

Abstract

Tetrabutylammonium decatungstate (TBADT) has emerged as a valuable photocatalyst for sunlight‐induced organic reactions. In this communication we wish to present its use for the photocatalytic oxidation of hydroxamic acids to generate fleeting nitrosocarbonyl intermediates. The reaction required a fine tuning of the conditions, especially in terms of solvent and additives, since an aqueous acetonitrile solution containing a mild base (NaHCO3) gave the best results. The obtained highly reactive nitrosocarbonyl species were then efficiently trapped with suitable dienes, such as cyclopentadiene and 1,3‐cyclohexadiene, to afford the corresponding Hetero Diels–Alder (HDA) cycloadducts in good yields. Dedicated photophysical experiments helped to elucidate the mechanistic scenario.

Recent advances in visible light-activated radical coupling reactions triggered by (i) ruthenium, (ii) iridium and (iii) organic photoredox agents

“…72 Tetrabutylammonium decatungstate (TBADT, 18) can be prepared in one step from tetrabutylammonium bromide and sodium tungstate (Scheme 13). 73 Alongside decatungstate catalyst, a manganese perchlorophthalocyanine catalyst has been used for C-H functionalisation. 74 These compounds will not be discussed in detail in this review.…”

Direct decarboxylative Giese reactions

“…58 As well as being efficient in HAT and oxidation reactions, TBADT has been shown to be a convenient and robust photocatalyst that can be readily synthesised. 59 As a member of the large family called polyoxometalates (POMs), 60 reduction of the anion gives rise to mixed-valence polyanions known as heteropoly blues, characterised by the extra electrons at the metal centres. This colour change to blue provides a convenient means for reaction monitoring.…”

Emerging Activation Modes and Techniques in Visible-Light-Photocatalyzed Organic Synthesis

“…Interestingly, the TBADT is commercially available and furthermore easily synthesized from tetrabutylammonium bromide and sodium tungstate in a single step (Scheme 4). 15 The selectivity of the reaction in Scheme 3 can be explained using the principles outlined in Figure 1. Due to the polar effect, the -methylene is disfavored in all aliphatic nitriles.…”

“…Interestingly, TBADT is commercially available and furthermore easily synthesized from tetrabutylammonium bromide and sodium tungstate in a single step (Scheme 4). 15 Scheme 4 Synthesis of tetrabutylammonium decatungstate (TBADT)…”