通过使用手性Ni II / N,N'-二氧化物络合物作为催化剂,已实现了对β,γ-不饱和α-酮酸酯的烯丙基硼酸的高度对映体选择性形式共轭烯丙基加成。该转化过程通过烯丙基硼化/ oxy-Cope重排序列进行,提供了简便且快速的途径,以中等至良好的收率(65-92%)和出色的ee值(90-99%ee)转化为γ-烯丙基-α-酮酸酯)。1,2-烯丙基化产物的分离提供了对随后oxy-Cope重排反应机理的认识:底物诱导的手性转移和手性Lewis酸加速过程。在实验研究和DFT计算的基础上,提出了一种罕见的船状过渡态模型,作为氧-科普重排过程中高手性转移的起源。
diastereo-, and enantioselective Diels–Alderreaction of β,γ-unsaturated α-ketoesters with (E)-1-phenyl dienes has been accomplished by using a stable and easily available chiral N,N′-dioxide/zinc(II) complex as catalyst. Only one isomer of the corresponding cyclohexenes with three chiral centers was obtained in good to excellent yields with excellent ee values under mild reaction conditions. The configurations
A highlyenantioselective Michael addition of allomaltol (5‐hydroxy‐2‐methyl‐4H‐pyran‐4‐one) to both aromatic and aliphatic β,γ‐unsaturated α‐ketoesters has been realized. Under the catalysis of a chiral bifunctional tertiary amine‐squaramide that bears a (1R,2R)‐1,2‐diphenylethane‐1,2‐diamine scaffold, the reaction proceeded smoothly with high levels of enantioselectivity to give the desired products
Michael Addition–Lactonization of Arylacetyl Phosphonate to β,γ-Unsaturated α-Keto Esters for the Synthesis of Chiral <i>syn</i>-3,4-Dihydropyranones and 5,6-Dihydropyranones
Catalytic asymmetric Michael addition–lactonization of arylacetyl phosphonates to β,γ-unsaturated α-ketoesters by a chiral bifunctional thiourea–tertiary amine was established. Using the developed protocol, a range of optically pure syn-3,4-dihydropyranones were generated in good yields with good to excellent stereoselectivities (up to >20:1 dr and 99% ee). Meanwhile, when stoichiometric diisopropylethylamine