Reaction of diazodiketoesters 17 and 28 with methyl glyoxylate in the presence of catalytic rhodium(II) acetate generates predominantly the 6,8-dioxabicyclo[3.2.1]octanes 29 and 30, respectively. Acid-catalysed rearrangement of the corresponding alcohol 31 favours, at equilibrium, the 2,8-dioxabicyclo[3.2.1]octane skeleton 33 of the squalestatinsâzaragozic acids. Force field calculations on the position of the equilibrium gave misleading results. DFT calculations were correct in suggesting that the energy difference between 31 and 33 should be small, but did not always suggest the right major product. Calculation of the NMR spectra of the similar structures could be used to assign the isomers with a high level of confidence.
二
氮二
酮酸酯17和28与
甲基乙二醛在催化性
醋酸铑(II)的存在下反应,主要生成6,8-二
氧双环[3.2.1]辛烷29和30。相应的醇31的酸催化重排在平衡时更倾向于形成鲨
烯类和萨拉戈酸的2,8-二
氧双环[3.2.1]辛烷骨架33。关于平衡位置的力场计算结果令人误解。密度泛函理论(DFT)计算正确地表明31与33之间的能量差应较小,但并不总是指示出正确的主要产物。对类似结构的核磁共振(NMR)谱的计算可以用来高
水平地确定异构体。