Dearomatized BIAN Alkaline-Earth Alkyl Catalysts for the Intramolecular Hydroamination of Hindered Aminoalkenes

Reaction of a sterically encumbered bis­(imino)­acenapthene (dipp-BIAN) with either potassium alkyl or the heavier alkaline-earth dialkyl [Ae­{CH­(SiMe₃)₂}₂(THF)₂] (Ae = Mg, Ca, Sr) reagents results in dearomatization of the aromatic ligand. The heteroleptic alkaline-earth alkyl species show enhanced stability toward Schlenk-type redistribution but undergo solution exchange when the bis­(trimethylsilyl)­methyl substituent is replaced by an anionic ligand of lower overall steric demands. In contrast, analogous reactions performed with [Ba­{CH­(SiMe₃)₂}₂(THF)₂] evidenced facile solution redistribution and resulted in an unusual C–C coupling reaction which is suggested to result from a sterically induced reductive process. An assessment of the Mg, Ca, and Sr alkyl compounds as precatalysts for the intramolecular hydroamination of aminoalkenes evidenced enhanced reactivity, which is ascribed to the greater solution stability of the catalytically active species. Most notably the calcium species may even be applied to the high-yielding cyclization of substrates bearing alkyl substitution at either of the alkenyl positions

Dearomatized BIAN Alkaline-Earth Alkyl Catalysts for the Intramolecular Hydroamination of Hindered Aminoalkenes

Reaction of a sterically encumbered bis­(imino)­acenapthene (dipp-BIAN) with either potassium alkyl or the heavier alkaline-earth dialkyl [Ae­{CH­(SiMe₃)₂}₂(THF)₂] (Ae = Mg, Ca, Sr) reagents results in dearomatization of the aromatic ligand. The heteroleptic alkaline-earth alkyl species show enhanced stability toward Schlenk-type redistribution but undergo solution exchange when the bis­(trimethylsilyl)­methyl substituent is replaced by an anionic ligand of lower overall steric demands. In contrast, analogous reactions performed with [Ba­{CH­(SiMe₃)₂}₂(THF)₂] evidenced facile solution redistribution and resulted in an unusual C–C coupling reaction which is suggested to result from a sterically induced reductive process. An assessment of the Mg, Ca, and Sr alkyl compounds as precatalysts for the intramolecular hydroamination of aminoalkenes evidenced enhanced reactivity, which is ascribed to the greater solution stability of the catalytically active species. Most notably the calcium species may even be applied to the high-yielding cyclization of substrates bearing alkyl substitution at either of the alkenyl positions

Stoichiometric and Catalytic Reactivity of <i>tert</i>-Butylamine–Borane with Calcium Silylamides

The primary amine–borane <i>t</i>-BuNH₂·BH₃ reacts with a β-diketiminate-supported silylamido calcium complex with elimination of HN­(SiMe₃)₂ and formation of the corresponding primary amidoborane complex, in which the deprotonated amine–borane is attached to the alkaline-earth center via its nitrogen atom and anagostic interactions with the boron-bound hydrides. Catalytic dehydrocoupling reactions employed with this β-diketiminate precatalyst are found to be slow and complicated by protonation of the supporting ligand and the formation of a number of boron-containing products, all of which have been positively identified. In common with previous studies of group 2 catalyzed secondary amine–borane dehydrogenation, the first formed major product of the catalysis is identified by solution NMR and solid-state single-crystal X-ray studies to be a cyclic diborazane, [H^tBuN–BH₂]₂, the formation of which is accompanied by variable proportions of diamidoborane and aminoborane products. The active calcium species is also observed to be depleted during the catalysis due to the formation of hydrocarbon-insoluble [Ca­(BH₄)₂·THF]_∞, which has also been structurally characterized. Continued heating of these reaction mixtures results in the formation of cyclic trimeric 1,3,5-tri-<i>tert</i>-butylborazine, which is proposed to form through the intermediacy of [H^tBuN–BH₂]₂ by an, as yet, undefined sequence of borazane dehydrogenation and ring expansion reactions

Total Synthesis of (+)-Grandifloracin by Iron Complexation of a Microbial Arene Oxidation Product

(+)-Grandifloracin was synthesized from sodium benzoate by means of a dearomatizing dihydroxylation that proceeds with unusual regioselectivity. Iron diene complexes formed from the arene oxidation product permit the use of otherwise inaccessible transformations. The synthetic material was shown to be antipodal to the natural product, thus determining the absolute configuration of grandifloracin for the first time

Total Synthesis of (+)-Grandifloracin by Iron Complexation of a Microbial Arene Oxidation Product

(+)-Grandifloracin was synthesized from sodium benzoate by means of a dearomatizing dihydroxylation that proceeds with unusual regioselectivity. Iron diene complexes formed from the arene oxidation product permit the use of otherwise inaccessible transformations. The synthetic material was shown to be antipodal to the natural product, thus determining the absolute configuration of grandifloracin for the first time

Radical Ring Opening Polymerization of Cyclic Ketene Acetals Derived From d‑Glucal

A cyclic ketene acetal (CKA) derived from d-glucal was synthesized, and its polymerization using free radicals has been investigated. NMR analysis of the resulting polymers revealed the formation of polyacetal–polyester copolymers, with up to 78% of ester linkages formed by radical ring-opening polymerization (rROP). Conversely, the polymerization of the monomer-saturated analogue only produced acetal linkages, demonstrating that the alkene functionality within the d-glucal pyranose ring is essential to promote ring-opening and ester formation, likely via the stabilization of an allyl radical. The thermal properties of the polymers were linked to the ratio of the ester and acetal linkages. Copolymerization with methyl methacrylate (MMA) afforded statistically PMMA-rich copolymers (66–98%) with linkages prone to hydrolytic degradation and decreased glass-transition temperatures. The retention of the pseudoglucal alkene function offers opportunities to functionalize further these bioderived (co)polymers

Radical Ring Opening Polymerization of Cyclic Ketene Acetals Derived From d‑Glucal

A cyclic ketene acetal (CKA) derived from d-glucal was synthesized, and its polymerization using free radicals has been investigated. NMR analysis of the resulting polymers revealed the formation of polyacetal–polyester copolymers, with up to 78% of ester linkages formed by radical ring-opening polymerization (rROP). Conversely, the polymerization of the monomer-saturated analogue only produced acetal linkages, demonstrating that the alkene functionality within the d-glucal pyranose ring is essential to promote ring-opening and ester formation, likely via the stabilization of an allyl radical. The thermal properties of the polymers were linked to the ratio of the ester and acetal linkages. Copolymerization with methyl methacrylate (MMA) afforded statistically PMMA-rich copolymers (66–98%) with linkages prone to hydrolytic degradation and decreased glass-transition temperatures. The retention of the pseudoglucal alkene function offers opportunities to functionalize further these bioderived (co)polymers

Synthesis of <i>N</i>‑alkoxycarbonyl Pyrroles from <i>O</i>‑Substituted Carbamates: A Synthetically Enabling Pyrrole Protection Strategy

The condensation of readily available O-substituted carbamates with 2,5-dimethoxytetrahydrofuran gives N-alkoxycarbonyl pyrroles in a single step and in good yield. By this method, several common amine protecting groups can be introduced on the pyrrole nitrogen. With the exception of N-Boc, N-alkoxycarbonyl groups have seen only minimal use for protection of the pyrrole nitrogen to date. Here, we show that N-alkoxycarbonyl protection can endow pyrrole with distinct reactivity in comparison with N-sulfonyl protection, for example, in a pyrrole acylation protocol employing carboxylic acids with a sulfonic acid anhydride activator

Xylose- and Nucleoside-Based Polymers via Thiol–ene Polymerization toward Sugar-Derived Solid Polymer Electrolytes

A series of copolymers have been prepared via thiol–ene polymerization of bioderived α,ω-unsaturated diene monomers with dithiols toward application as solid polymer electrolytes (SPEs) for Li+-ion conduction. Amorphous polyesters and polyethers with low Tg’s (−31 to −11 °C) were first prepared from xylose-based monomers (with varying lengths of fatty acid moiety) and 2,2′-(ethylenedioxy)diethanethiol (EDT). Cross-linking by incorporation of a trifunctional monomer also produced a series of SPEs with ionic conductivities up to 2.2 × 10–5 S cm–1 at 60 °C and electrochemical stability up to 5.08 V, a significant improvement over previous xylose-derived materials. Furthermore, a series of copolymers bearing nucleoside moieties were prepared to exploit the complementary base-pairing interaction of nucleobases. Flexible, transparent, and reprocessable SPE films were thus prepared with improved ionic conductivity (up to 1.5 × 10–4 S cm–1 at 60 °C), hydrolytic degradability, and potential self-healing capabilities

Xylose- and Nucleoside-Based Polymers via Thiol–ene Polymerization toward Sugar-Derived Solid Polymer Electrolytes

A series of copolymers have been prepared via thiol–ene polymerization of bioderived α,ω-unsaturated diene monomers with dithiols toward application as solid polymer electrolytes (SPEs) for Li+-ion conduction. Amorphous polyesters and polyethers with low Tg’s (−31 to −11 °C) were first prepared from xylose-based monomers (with varying lengths of fatty acid moiety) and 2,2′-(ethylenedioxy)diethanethiol (EDT). Cross-linking by incorporation of a trifunctional monomer also produced a series of SPEs with ionic conductivities up to 2.2 × 10–5 S cm–1 at 60 °C and electrochemical stability up to 5.08 V, a significant improvement over previous xylose-derived materials. Furthermore, a series of copolymers bearing nucleoside moieties were prepared to exploit the complementary base-pairing interaction of nucleobases. Flexible, transparent, and reprocessable SPE films were thus prepared with improved ionic conductivity (up to 1.5 × 10–4 S cm–1 at 60 °C), hydrolytic degradability, and potential self-healing capabilities