Fig. 1. ¹³C NMR Spectra of the reaction mixtures with 200 mM ¹³C-labelled KCN, 200 mM Na₂SO₃ and 100 mM ¹³C-labelled formaldehyde (in 10% D₂O in H₂O). (a) ¹³C-Labelled 11; (b) as (a), then mixed with ¹³C-labelled KCN and NaH₂PO₄ at pH 7; (c) the mixture from (b) after irradiation at 254 nm for 12.5 h; (d) the mixture from (c) after sparging with argon for 13 h.