To demonstrate the technique, 30 mg (0.25 mmol) of [1-13 C, 2,3-d 2 ]-fumaric acid (Sigma-Aldrich) and 18.1 mg (0.025 mmol) of the [Rh(dppb)(COD)]BF 4 catalyst were dissolved in methanol-d 4 (5 mL). 50%-para-enriched H 2 was prepared by passing hydrogen gas at a pressure of 10 bar over iron oxide at 77 K. Each experimental run started by transferring 250 µL of the stock solution to a high-pressure NMR tube and heating the sample to 75 ○ C in the ambient magnetic field of the laboratory (110 µT). The heated sample was transferred to a magnetically shielded chamber (three concentric walls of mu-metal, from Twinleaf LLC, USA) equipped with magnetic field coils. Paraenriched hydrogen gas was dissolved in the solution by bubbling. This initiated the catalytic hydrogenation of the [1-13 C, 2,3-d 2 ]fumaric acid precursor, generating the singlet-polarized target substance [1-13 C, 2,3-d 2 ]-succinic acid. As discussed below, several methods were evaluated for the conversion of the proton singlet order into hyperpolarized 13 C magnetization. Immediately after singlet-to-magnetization conversion, the level of 13 C polarization was assessed by rapidly inserting the sample into a conventional 9.41 T NMR magnet, followed by generation of the 13 C NMR spectrum by applying a single π/2 pulse and Fourier transformation of the free-induction decay. Further details of the experimental implementation are given in the supplementary information.