Chiral dendrigraft polymer for asymmetric synthesis of isoquinuclidines

Abstract

The synthesis of multi-arm star dendrigraft amidoamine polymer with pentaerythritol initiated polyepichlorohydrin as the core, PEN-G₂, on a solid resin support has been demonstrated. We have functionalized a Merrifield resin support with polyepichlorohydrin, and dendrons are grown on it up to second generation using a “graft from” approach. The estimation of amine functionality was done and found to be 25 mmol g⁻¹ which was 70% of the theoretical value. Photolytic cleavage of the dendrigraft polymer from the support resulted in a brown water-soluble viscous liquid. The molecular weight of 3966 shows that out of the 9 G₁ dendritic substituents, 5 of them were converted to generation G₂. The TEM image of the G₂ polymer shows an inhomogeneous polygon-like appearance. The chiral modification of the dendrigraft polymer, PEN-G₂, has been done. The copper complex of chiral modified PEN-G₂ dendrigraft polymer was synthesized and characterized. The copper complex of PEN-G₂ dendrigraft polymer was found to be an excellent catalyst for the synthesis of isoquinuclidines via aza Diels–Alder reaction between cyclohexenone and imines. The catalyst exhibited superior enantioselectivity. The reusability of the catalyst was studied for five reaction cycles.