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.