A Catalytic Route to Ampakines and Their Derivatives

A catalytic domino reaction that efficiently provides access to an important class of heterocycles, the ampakines, is reported. Our approach is based on the cobalt-catalyzed hydroformylation of dihydrooxazines and allows for the facile synthesis of the pharmaceutically interesting compound CX-614 and related substances

Synthesis and Characterization of Alternating and Multiblock Copolymers from Ethylene and Cyclopentene

The synthesis and characterization of copolymers from ethylene and cyclopentene are reported. Polymerization of ethylene and cyclopentene using a living bis(phenoxyimine)titanium catalyst yields copolymers with cis-1,2 cyclopentane units, high molecular weights, and low polydispersities. The effects of cyclopentene concentration, ethylene pressure, and reaction temperature on cyclopentene incorporation were determined; under the optimal reaction conditions 47 mol % cyclopentene was incorporated to give a nearly perfectly alternating copolymer. The glass-transition temperatures of the polymers, ranging from −27.3 °C (27 mol % cyclopentene) to 10.1 °C (47 mol % cyclopentene), were found to be linearly dependent on the mole percent cyclopentene content. Synthesis of atactic and isotactic model poly(ethylene-alt-(cis-1,2-cyclopentane))s using ring-opening metathesis polymerization allowed the assignment of the fine structure of 13C NMR spectra of atactic polymers made from ethylene and cyclopentene. Finally, polymers containing blocks with varying ratios of ethylene/cyclopentene were synthesized. By repetitively raising and lowering the ethylene pressure of a cyclopentene/ethylene polymerization, polymers with multiple blocks were synthesized

Carbonylation of <i>cis</i>-Disubstituted Epoxides to <i>trans</i>-β-Lactones: Catalysts Displaying Steric and Contrasteric Regioselectivity

<i>trans</i>-β-Lactones are a versatile and useful class of compounds, but reliable methods for their direct synthesis are still limited. Addressing this problem, we present herein two catalysts for the regioselective carbonylation of <i>cis</i>-disubstituted epoxides. The two catalysts show high activities and opposing regioselectivities so that either one of the two possible β-lactone regioisomers can be obtained selectively

A Catalytic Route to Ampakines and Their Derivatives

A catalytic domino reaction that efficiently provides access to an important class of heterocycles, the ampakines, is reported. Our approach is based on the cobalt-catalyzed hydroformylation of dihydrooxazines and allows for the facile synthesis of the pharmaceutically interesting compound CX-614 and related substances

Ring-Opening Copolymerization of Maleic Anhydride with Epoxides: A Chain-Growth Approach to Unsaturated Polyesters

We report the ring-opening copolymerization of maleic anhydride with a variety of epoxides catalyzed by a chromium(III) salen complex. Quantitative isomerization of the cis-maleate form of all polymers affords the trans-fumarate analogues. Addition of chain transfer reagents yields low Mn, narrow PDI polymer samples. This method provides access to a range of new unsaturated polyesters with versatile functionality, as well as the first synthesis of high molecular weight poly(propylene fumarate)

Insertion/Isomerization Polymerization of 1,5-Hexadiene: Synthesis of Functional Propylene Copolymers and Block Copolymers

Polymerization of 1,5-hexadiene with a bis(phenoxyimine) titanium catalyst system is reported. The microstructure of the polymer contains the expected methylene-1,3-cyclopentane units as well as the unexpected 3-vinyl tetramethylene units. A mechanism for formation of this polymer is proposed. This unusual reaction is also employed in the synthesis of vinyl-functional polypropylene copolymers and block copolymers with low polydispersity indices

Carbonylative Polymerization of Propylene Oxide: A Multicatalytic Approach to the Synthesis of Poly(3-Hydroxybutyrate)

We report a highly efficient method for the synthesis of poly(3-hydroxybutyrate) by the carbonylative polymerization of propylene oxide. The use of compatible epoxide carbonylation and lactone polymerization catalysts allows for a one-pot reaction that eliminates the need to isolate and purify the toxic β-butyrolactone intermediate

Stereoselective Ring-Opening Polymerization of <i>meso</i>-Lactide: Synthesis of Syndiotactic Poly(lactic acid)

Stereoselective Ring-Opening Polymerization of meso-Lactide:  Synthesis of Syndiotactic Poly(lactic acid

Pairing-Enhanced Regioselectivity: Synthesis of Alternating Poly(lactic-<i>co</i>-glycolic acid) from Racemic Methyl-Glycolide

Poly­(lactic-co-glycolic acid) (PLGA) is used in vivo for various biomedical applications. Due to its biodegradability and biocompatibility, PLGA is uniquely suited for controlled drug delivery with parenteral administration. Previously, we established the synthesis of isotactic, alternating PLGA from enantiopure starting materials. Here, to fill in the gap of the current field, we have developed the synthesis of syndioenriched, alternating PLGA from racemic methyl-glycolide (rac-MeG). The synthesis of alternating PLGA is accomplished by a highly regioselective ring-opening polymerization of rac-MeG with an optimized racemic aluminum catalyst. Mechanistic studies are carried out to elucidate the pairing-enhanced catalyst regio- and stereocontrol. Polymer sequence fidelity has been established by NMR investigations, confirming a high degree of alternation of the comonomer sequence and moderate syndiotacticity within the backbone stereoconfiguration. The resulting syndioenriched material is amorphous, which will facilitate the drug complexation behavior

Synthesis and Polymerization of Norbornenyl-Terminated Multiblock Poly(cyclohexene carbonate)s: A Consecutive Ring-Opening Polymerization Route to Multisegmented Graft Polycarbonates

We report a method for the synthesis of multisegmented polycarbonate graft copolymers. Using a β-diiminate zinc catalyst with a norbornene carboxylate initiator, we achieved living block copolymerizations of functionalized cyclohexene oxides and CO₂, yielding norbornenyl-terminated macromonomers with variable block sequences. Subsequent ring-opening metathesis polymerization of the norbornenyl-terminated macromonomers produced segmented graft copolymers. This method provides a facile route to core–shell structures with readily controllable molecular parameters