The reaction of α- and ω-methylenelactams with nitrones. Influence of electronic and geometric factors on the stereoselectivity of their 1,3-dipolar cycloaddition
作者:Séverinne Rigolet、Jean Marie Mélot、Joel Vébrel、Angèle Chiaroni、Claude Riche
DOI:10.1039/b000129p
日期:——
Various four to six-membered ring α- and Ï-methylenelactams 1â5 were reacted with nitrones 6 and afforded good yields of spiroadducts 7â12 through a regiospecific [3 + 2] cycloaddition. Owing to the creation of at least two new asymmetric centres, mixtures of diastereoisomers were usually obtained whose structures were established by two-dimensional NOESY experiments or X-ray crystallography. Among the dipolarophiles, 3-methyleneazetidin-2-ones 1 yielded adducts with a very high stereoselectivity. A similar behaviour was also observed with α-benzoylnitrone 6a as a 1,3-dipole. Electronic and geometric interactions of the reagents 1â5 and 6 in the course of the cycloaddition process were discussed in order to account for the experimental stereochemical outcomes.
各种四到六元环的α-和ω-亚甲基内酰胺1–5与硝醇6反应,通过区域特异性[3 + 2]环加成反应获得了良好产率的螺环加成物7–12。由于形成了至少两个新的不对称中心,通常会得到包括邻异构体在内的混合物,其结构通过二维NOESY实验或X射线晶体学确定。在极性体中,3-亚甲基氮杂环丁烯-2-酮1产生的加成物具有非常高的立体选择性。用α-苯甲酰硝醇6a作为1,3-偶极体时,也观察到类似的行为。在环加成过程中,还讨论了试剂1–5和6的电子与几何相互作用,以解释实验的立体化学结果。