The molecular and crystal structure of 1,3,3,5-tetraphenylpentane-1,5-dione (I) obtained from direct methods and anisotropically refined by the least-squares method shows that the two 3,3-phenyl groups force the molecule into a conformation suitable for formation of cyclic products and intermediates. Compound I crystallizes in P1 group with lattice parameters a = 8.444(1), b = 10.195(2), c = 14.618(2) Å, α = 75.52(2)°, β = 73.22(1)°, γ = 65.47(1)°. Photochemically and thermally found was the system I ↔ II. The reaction of 1,5-dione I with phenylmagnesium bromide gives the 2,3-dihydropyran derivative III, whereas complex hydrides give a mixture of IV and VI. On treatment with magnesium, the diketone I gives diol VIII. Chlorine (Cl2) reacts with compound I to give the mono-, di-, and tetrachloro derivatives XII, XIII, and XIV, respectively. Bromine (Br2) produces 3,5-dibromo-4H-pyran derivative XVIII, whereas I2 only catalyzes the formation of 4H-pyran V. The formylation of dione I with dimethylformamide and POCl3 gives the 4H-pyran-3-carbaldehyde XX. Probable mechanisms of the reactions investigated and the stereochemistry of compounds VI, VIII, XIII, and XIV are discussed.
1,3,3,5-四苯基戊二酮(I)的分子和晶体结构是通过直接方法获得的,并通过最小二乘法进行各向异性精修,结果显示两个3,3-苯基团迫使分子呈适合形成环状产物和中间体的构象。化合物I以P1群结晶,晶格参数a = 8.444(1) Å,b = 10.195(2) Å,c = 14.618(2) Å,α = 75.52(2)°,β = 73.22(1)°,γ = 65.47(1)°。光化学和热化学发现了体系I↔II。1,5-二酮I与溴化苄镁反应得到2,3-二氢吡喃衍生物III,而复杂的氢化物给出混合物IV和VI。经镁处理,二酮I生成二醇VIII。氯气(Cl2)与化合物I反应得到单氯、二氯和四氯衍生物XII、XIII和XIV。溴气(Br2)产生3,5-二溴-4H-吡喃衍生物XVIII,而I2仅催化4H-吡喃V的形成。用二甲基甲酰胺和POCl3对二酮I进行甲酰化反应得到4H-吡喃-3-甲醛XX。讨论了所研究反应的可能机理以及化合物VI、VIII、XIII和XIV的立体化学。