Catalytic Synthesis of Phthalide Derivatives via Asymmetric Bromolactonization of Stilbene‐type Carboxylic Acids usingN,N‐Dibenzyl Diaminomethylenemalononitrile as Organocatalyst

Abstract

The asymmetric 5‐exo bromolactonization of stilbene‐type carboxylic acids could be achieved using a N,N‐dibenzyl diaminomethylenemalononitrile organocatalyst with high yields and excellent enantioselectivities (up to 92% ee) of the corresponding phthalide derivatives. This is the first report where the successful synthesis of the phthalide derivatives as the main product, with high optical purity, could be achieved using the asymmetric 5‐exo bromolactonization of the stilbene‐type carboxylic acids with various substituents.

5-exo-Selective asymmetric bromolactonization of stilbenecarboxylic acids catalyzed by phenol-bearing chiral thiourea

“…Although there is room for improvement in enantio- and regioselectivity, a higher regioselectivity was accomplished in the reaction of 1 without an EWG than those reported in previous studies. 22,23 Further applications of this catalyst in other asymmetric reactions are currently being explored by our group.…”

“…22 Miura recently reported the first 5- exo -selective asymmetric bromolactonization of 1 without an EWG. 23 However, the regioselectivity in the reactions of these substrates was up to 2 : 1.…”