Polymerization Amplified Stereoselectivity (PASS) of Asymmetric Michael Addition Reaction and Aldol Reaction Catalyzed by Helical Poly(phenyl isocyanide) Bearing Secondary Amine Pendants

Abstract

A novel enantiopure phenyl isocyanide (1) carrying tert-butyloxycarboryl (Boc) protected L-prolinol ester was designed and synthesized. Living polymerization of 1 using a alkyne−Pd(II) catalyst afforded helical poly-1 m s in high yields with controlled molecular weights (M n s) and narrow molecular weight distributions (M w /M n s). Removing the protecting Boc groups on the L-prolinol ester pendants lead to the formation of helical poly-2 m , which showed high optical activity owing to the preferred left-handed helix of polyisocyanide main chain. The poly-2 m s showed excellent catalytic ability on asymmetric Michael addition reaction. Both the enantiomeric excess (ee) and diastereomeric ratio (dr) values of the product were linearly correlated to the M n and optical activity of poly-2 m . Increasing the M n of poly-2 m s will amplify the stereoselectivity of the asymmetric Michael addition reaction until the M n reached to 44.9 kDa, revealing the polymerization amplified stereoselectivity (PASS) behavior of the asymmetric reaction. Under optimized the reaction condition, the ee and dr values of the Michael addition reaction product can be up to 99% and >99/1, respectively. Poly-2 200 can be easily recovered and reused in the Michael addition reaction for at least 5 cycles without loss of its activity and stereoselectivity significantly. The poly-2 200 can also be used to catalyze the asymmetric aldol reaction. The ee and dr values of the model aldol reaction were respectively up to 99% and >99/1. Moreover, the poly-2 200 can be facilely recovered and alternatively catalyzed Michael addition reaction and aldol reactions for at least six cycles with maintained selectivity and activity.

Helicity Induction and Its Static Memory of Poly(biphenylylacetylene)s Bearing Pyridine N‐Oxide Groups and Their Use as Asymmetric Organocatalysts

“…The application of optically active helical polymers for asymmetric catalysis has also attracted growing interest, because a one‐handed helical chirality can significantly contribute to the enantioselectivity due to a one‐handed helical arrangement of the catalytically active, chiral/achiral units along the one‐handed helical polymer backbone . Up to now, a variety of helical polymer‐based asymmetric catalysts have been developed mainly by introducing catalytically active, chiral/achiral units as components in or along artificial helical polymers that involve polyacetylenes, poly(methacrylate)s, polyisocyanates, polyisocyanides, and poly(quinoxaline‐2,3‐diyl)s . In these cases, the use of optically active monomers is essential to control their helical handedness except for poly(methacrylate)s with a bulky pendant prepared by helix‐sense‐selective polymerization using chiral catalysts or initiators .…”

Super Chirality Promotion of Helical Poly(Phenyl Isocyanide)s by Grafting onto Ethyl Cellulose

“…The higher CD value for PPI 50 (CD = 21) compared to that of PPI 20 (CD = 18) suggests a relatively stable and stereoregular helix conformation caused by the relatively long chain length of PPI 50 . [ 38 ] Importantly, their corresponding copolymers of EC‐2,3‐g‐PPI 20 and EC‐2,3‐g‐PPI 50 also showed a dramatically enhanced Cotton effect at the same wavelength, with a CD value increase of 146% and 302% compared to those of PPI 20 and PPI 50 , respectively. The CD value also increased by the grafting degree of PPI 50 on EC‐2,3‐g‐PPI 50 , which is apparent in Figure 6C.…”

Synthesis of polymer microsphere‐supported chiral pyrrolidine catalysts by precipitation polymerization and their application to asymmetric Michael addition reactions

“…Wu et al reported the synthesis of helical poly(phenyl isocyanide) bearing L-prolinol derivative as pendant by living polymerization with controlled molecular weights and narrow molecular weight distributions. 36 The helical polymeric catalysts were applied to an asymmetric Michael addition and an aldol reaction. The catalytic activity was linearly correlated with the molecular weight (M n ) and optical activity of the polymeric catalyst.…”

“…The polymeric catalyst could be successfully reused several times with little change in yield and only small losses in selectivity. Wu et al reported the synthesis of helical poly(phenyl isocyanide) bearing l ‐prolinol derivative as pendant by living polymerization with controlled molecular weights and narrow molecular weight distributions 36 …”