Polyurethanes themselves are applied as flexible/rigid foams, adhesives, coatings and elastomers, as well as in many other areas. The primary application for the polymer products is as low-molecular-weight ( M n), (poly)hydroxyl-terminated ‘polyols’, which are widely used in the manufacture of polyurethanes. Depending on the epoxide and the selectivity of the catalyst, up to 31% (polycyclohexene carbonate) or 43% (polypropylene carbonate) of the polymer mass derives from CO 2. The most commonly studied epoxides are cyclohexene oxide (CHO) and propylene oxide (PO). The ROCOP reaction is a rare example of a truly catalytic process with the potential to deliver large-scale quantities of product, which genuinely consumes carbon dioxide. The ROCOP of carbon dioxide and epoxides to produce aliphatic polycarbonates. The intention is not to provide a comprehensive review of all known catalysts indeed, such reviews are already available. The focus for this review article will be to highlight and exemplify some of the key findings in this area of catalysis, in particular using examples drawn from our own research. The ROCOP process is strongly dependent on the selection of the catalyst, with various homogeneous and heterogeneous catalysts having been reported. However, it remains important to pursue CO 2 utilization as a means to reduce emissions, particularly those associated with existing, large-scale industrial processes and as an economic driver to support carbon capture. It should be made clear that the use of CO 2 in any chemical manufacturing process is unable to make a large impact on overall CO 2 levels in the atmosphere. The reaction was discovered more than 40 years ago and has since continued to attract attention as a means to reduce pollution associated with polymer manufacture and to ‘add value’ to carbon dioxide. This Account summarizes our research on metal-catalyzed directed ring-opening reactions of epoxides, which encompasses the following breakthroughs: (1) highly regioselective ring-opening of various substrates including epoxy allylic alcohols, epoxy homoallylic alcohols and epoxy allylic sulfonamides with a variety of N-, O-, and halide-nucleophiles catalyzed by W-, Mo-, or Ni-salt (2) first kinetic resolutions of epoxy allylic alcohols, epoxy homoallylic alcohols, and epoxy allylic sulfonamides with various amines as nucleophiles, which were catalyzed by W-bishydroxamic acid (W-BHA), nickel-BINAM, and Gd-N,N'-dioxide catalytic system, respectively (3) successful implementation of the strategy of combined asymmetric syntheses by the combination of the enantioselective epoxidation and the enantioselective ring-opening of 2,3-epoxy alcohols establishing a new entry to prepare amino alcohols in regio-, diastereo-, and enantiomerically pure form.The ring-opening copolymerization (ROCOP) of carbon dioxide and epoxides is an interesting method to synthesize a range of aliphatic polycarbonates ( figure 1). Based on our successful results of regioselective ring-opening of functionalized epoxides by implementing the directed ring-opening strategy, we also investigated the enantioselective ring-opening of internal epoxides bearing a functional moiety as directing group. In these cases, the issue of regiocontrol of the ring-opening is circumvented or minimized. However, excellent results are usually obtained in the case of the kinetic resolution of terminal epoxides or the desymmetrization of meso-epoxides. Alternatively, asymmetric ring-opening of epoxides can also provide the ring-opening products in highly enantioenriched form. To address this challenge, our approach is to use the readily available functional moiety incorporated in an epoxide as a directing group to realize the regioselective nucleophilic attack on the oxirane ring. Regioselective ring-opening of epoxides with substituents on both sides demonstrating similar steric and electronic effects is still a formidable challenge for organic chemists. However, prior to our research work, the scope of catalytic highly regioselective ring opening of epoxides is limited to structurally or electronically biased epoxides, such as terminal and aromatic epoxides. Regioselective and enantiospecific ring opening of readily available enantioenriched epoxides precursors provides a straightforward access to diverse highly functionalized molecules which can serve as chiral building blocks for synthesis of biologically active compounds. Control of regio- and stereoselectivity of chemical reactions is the central theme in synthetic chemistry.
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