The current insufficient recycling of commodity polymer waste has resulted in pressing environmental and human health issues in our modern society. In the quest for next-generation polymer materials, chemists have recently shifted their attention to the design of chemically recyclable polymers that can undergo depolymerization to regenerate monomers under mild conditions. During the past decade, ring-closing metathesis reactions have been demonstrated to be a robust approach for the depolymerization of polyolefins, producing low-strain cyclic alkene products which can be repolymerized back to new batches of polymers. In this review, we aim to highlight the recent advances in chemical recycling of polyolefins enabled by ring-closing metathesis depolymerization (RCMD). A library of depolymerizable polyolefins will be covered based on the ring size of their monomers or depolymerization products, including five-membered, six-membered, eight-membered, and macrocyclic rings. Moreover, current limitations, potential applications, and future opportunities of the RCMD approach will be discussed. It is clear from recent research in this field that RCMD represents a powerful strategy towards closed-loop chemical recycling of novel polyolefin materials.
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Selective ring-rearrangement or ring-closing metathesis of bicyclo[3.2.1]octenes
Explored was the competitive ring-closing metathesis vs. ring-rearrangement metathesis of bicyclo[3.2.1]octenes prepared by a simple and convergent synthesis from bicyclic alkylidenemalono-nitriles and allylic electrophiles. It was uncovered that ring-closing metathesis occurs exclusively on the tetraene-variant, yielding unique, stereochemically and functionally rich polycyclic bridged frameworks, whereas the reduced version (a triene) undergoes ring-rearrangement metathesis to 5 – 6 – 5 fused ring systems resembling the isoryanodane core.
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- NSF-PAR ID:
- 10224438
- Date Published:
- Journal Name:
- Chemical Communications
- Volume:
- 56
- Issue:
- 79
- ISSN:
- 1359-7345
- Page Range / eLocation ID:
- 11779 to 11782
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Sanglifehrin A and B are immunosuppressive macrocyclic natural products endowed with and differentiated by a unique spirocyclic lactam. Herein, we report an enantioselective total synthesis and biological evaluation of sanglifehrin A and B and analogs. Access to the spirocyclic lactam was achieved through convergent assembly of a key pyranone intermediate followed by a stereo‐controlled spirocyclization. The 22‐membered macrocyclic core was synthesized by ring‐closing metathesis in the presence of 2,6‐bis(trifluoromethyl) benzeneboronic acid (BFBB). The spirocyclic lactam and macrocycle fragments were united by a Stille coupling to furnish sanglifehrin A and B. Additional sanglifehrin B analogs with variation at the C40 position were additionally prepared. Biological evaluation revealed that the
2‐CF3 analog of sanglifehrin B exhibited higher anti‐proliferative activity than the natural products sanglifehrin A and B in Jurkat cells. Both natural products induced higher‐order homodimerization of cyclophilin A (CypA), but only sanglifehrin A promoted CypA complexation with inosine‐5′‐monophosphate dehydrogenase 2 (IMPDH2). The synthesis reported herein will enable further evaluation of the spirolactam and its contribution to sanglifehrin‐dependent immunosuppressive activity.
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/d0cc04624h
