Controlled Synthesis of One-Handed Helical Polymers Carrying Achiral Organoiodine Pendants for Enantioselective Synthesis of Quaternary All-Carbon Stereogenic Centers

Abstract

Inspired by highly efficient and enantioselective reactions catalyzed by biomacromolecules, developing artificial helical polymer-based catalysts for enantioselective reactions is an interesting work. In this work, a series of one-handed helical polyisocyanides bearing aryl iodine pendants were readily produced via asymmetric polymerization of achiral isocyanides using chiral Pd(II)-catalysts. Despite the inexistence of any stereogenic centers, these polymers showed large optical activity owing to the one-handed helicity. Remarkably, these polymers could catalyze asymmetric dearomatization spirocyclization of 1-hydroxy-N-aryl-2-naphthamide derivatives and gave chiral spirooxindole products with high enantioselectivity. The enantioselectivity was contributed by the helicity of the polyisocyanide backbone; helical polyisocyanides in opposite helicity produced the enantiomeric antipode products with comparable yields and similar high enantioselectivity. Thanks to the high molecular weight, the helical polymer catalysts could be recycled 10 times with maintained activity and stereoselectivity.

Achiral organoiodine-functionalized helical polyisocyanides for multiple asymmetric dearomative oxidations

“…A mechanism for the helical polyisocyanide catalyzed asymmetric reactions was proposed (Fig. 5a) [62][63][64] . Taking the asymmetric Kita-Spirocyclization as an example, the phenyl iodine pendants of polyisocyanide were initially oxidized to active hypervalent iodane (IA) by mCPBA.…”

Cobalt(iii)–salen decorated stereoregular optically active helical polyisocyanides enable highly effective cooperative asymmetric catalysis toward the kinetic resolution of epoxides

“…Our recent work has revealed that these types of helical polymers can act as polymer-supported catalysts for asymmetric catalysis and amplify a chiral environment. [65][66][67][68] Based on our long-term research interest in polyisocyanide chemistry and cooperative catalysis, 33,69,70 we hypothesized that optically active polyisocyanides could provide a highly tunable platform to realize asymmetric cooperative catalysis for kinetic resolution. In our molecular design of these chiral polymer-supported catalysts, the Co(III)-salen unit is decorated onto the pendant group of optically active polyisocyanides via living/control coordination polymerization of isocyanide monomers containing the salen moiety and then post-metalation of the Co(III) ion (Fig.…”

3D mesoporous polycalix-functionalized dual Brønsted–Lewis acidic double-charged DABCO-based ionic liquid: a powerful and recyclable supramolecular polymeric catalyst for the synthesis of spiro-fused[4H-pyran]

“…92,93 Although previously published approaches using a homogenous catalyst for preparing spiro derivatives are valuable, these catalysts suffer from some disadvantages, such as high cost, drastic separation from the reaction mixture, long-duration reaction, and high temperature. 94–99 Over recent years, various heterogenized organic polymer catalysts based on helical polymers (single-handed helical polyisocyanides), 100 polyethyleneglycols (PEG-Ni NPs, PEG-OSO 3 H), 101,102 polystyrene (PS@GO-Fe 3 O 4 ), 86 chitosan (Fe 3 O 4 @CS-SO 3 H NPs, Bmim(OH)/chitosan/C 2 H 5 OH), 103,104 cellulose (cellulose-SO 3 H, nano-cellulose-SbCl 5 , Cu 2 O@MCC, NiII(BAPTE)(NO 3 ) 2 -Cell nanocatalyst), 105–108 polyaniline (PANI/Fe 3 O 4 /CNT), 109 and collagen protein (Fe 3 O 4 @SiO 2 /ECH/IG) 110 have been used in the synthesis of spiro-fused[4 H -pyran]. Although the above-mentioned catalytic systems can be readily separated, the recycling times were low (probably due to leaching or tedious workup).…”