Scheme 1.

1,1‐Ethenediol (1) generated from malonic acid (2) through pyrolysis and trapping in an argon matrix. Subsequent photorearrangement to acetic acid (3) and ketene (4). Biologically highly relevant enols (5–7).

1,1‐Ethenediol (1) generated from malonic acid (2) through pyrolysis and trapping in an argon matrix. Subsequent photorearrangement to acetic acid (3) and ketene (4). Biologically highly relevant enols (5–7).