Unexpected Simple and Catalyst‐Free Condensation Reaction of Spiro Dihydrofurans with 2, 4‐Dinitrophenylhydrazine, Thiosemicarbazide, and Hydroxylamine for the Synthesis of Novel Corresponding 4, 4, 6′, 6′‐Tetramethyl‐3′‐aryl‐3′, 5′, 6′, 7′‐tetrahydrospiro[cyclohexane‐1, 2′‐indole]‐4′, 6(1′H)‐diones: Crystal Structure. (11th September 2018)