We describe the design and synthesis of a novel bis-dioxirane (3,3'-dimethyl-[3,3']bidioxirane, 1) and 1-(3-methyl-dioxiran-3-yl)-ethanone (2) from a -15 °C biacetyl–oxone mixture using a low temperature separation of the organic-soluble fraction. Evidence for unstable 1 and 2 was obtained with low temperature ¹H, ¹³C, HMBC NMR spectroscopy and is consistent with the predicted GIAO-B3LYP/6-31+G(d) calculations. The reaction showed the generation of carbon dioxide, acetic anhydride, acetic acid, and trace carbonyl products and their hydrates. Computational and experimental evidence suggest the participation of acyloxy and alkyl radicals in the decomposition reaction. One can use bis-dioxirane 1 to explore the boundaries of dioxirane stability in organic chemistry. This system provides a model for the discussion of proximity effects in dioxiranes and examines the nature of vicinal dioxirane chemical bonds.