Laurencione was isolated from Laurencia spectabilis and its structure determined to be an equilibrium mixture of (±)-2-hydroxy-2-methyldihydrofuran-3-one and 5-hydroxy-2,3-pentanedione. On silica gel, laurencione dimerized to optically inactive, crystalline spiro-bis-pinnaketal, a previously reported natural product of L. pinnatifida.