Oxalates, as the acid or Cs-salt 23 were prone to hydrolysis under reaction conditions and parallel screening of conditions did not provide a productive reaction (Supporting Scheme S2 and Table ). We hence examined oxetane carboxylic acids. Carboxylic acids have been extensively used in the formation of tertiary radical centers under photocatalytic conditions. 18b, Aryloxetane carboxylic acids were not available and prompted our recent report on their short two-step synthesis from 3-aryl-oxetan-3-ols involving catalytic Friedel-Crafts reaction followed by mild oxidative cleavage. Initial investigations with acid 1 were based on a report by MacMillan in 2014, which generated C(sp 3 ) radicals under decarboxylative photoredox conditions and trapped these with electron deficient alkenes. Electron-rich oxetane acid 1 was used as model substrate and ethyl acrylate as radical acceptor. The major product of this reaction was 3,3-disubstituted oxetane 2a, which was formed alongside di-alkylated product 2a', dimer 3 and reduced product 4. After ), desired 3,3-disubstituted oxetane 2a was obtained in 61% yield (± 5%, 95% confidence interval, n = 6, performed by three different chemists; Table , entry 1), with minimized formation of side products (3, 4) and finally little deviation from the MacMillan conditions. The mass balance in the standard reaction between 1 and ethyl acrylate was variable depending on the purity of 1 used (c.f. Table entry 1 and Supporting Table ). Nonetheless, complete conversion of starting material 1 is always observed. Deviations from an overall conserved mass balance of 100% are ascribed to intractable degradation products from the oxetane radical. a Reactions run on a 0.2 mmol scale under argon. Yield calculated by analysis of the 1 H NMR spectrum of the crude mixture of the reaction using 1,3,5-trimethoxybenzene as internal standard and a 30 s relaxation delay (d1). b Reported yields are the mean average of 6 experiments, isolated yields of a single run are in parentheses. Yields vs ethyl acrylate.