The combination of triazole/gold (TA‐Au) and Cu(OTf)2is identified as the optimal catalytic system for promoting intramolecular hydroboration for the synthesis of a six‐membered cyclic amine–borane. Excellent yields (up to 95 %) and regioselectivities (5‐exo vs. 6‐endo) were achieved through catalyst control and sequential dilution. Good functional‐group tolerance was attained, thus allowing the preparation of highly functionalized cyclic amine–borane substrates, which could not be achieved using other methods. Deuterium‐labeling studies support the involvement of a hydride addition to a gold‐activated alkyne with subsequent C−B bond formation.
Design and synthesis of stable four-coordinated benzotriazole-borane with tunable fluorescence emission
A new class of stable four-coordinated benzotriazole-borane compounds was developed via gold-catalyzed alkyne hydroboration. The application of polymeric (BH 2 CN) n reagent gave the formation of cyano-amine-boranes (CAB) complexes with less basic N-heterocyclic amines and anilines. Various new CABs were investigated in catalytic hydroboration to synthesize N–B cycles. The 1,2,3-benzotriazoles were identified as the only feasible N-source, giving the four coordinated borane N–B cycles (BTAB) in excellent yields (up to 90%) with good functional group tolerability. This new class of polycyclic N–B compounds showed excellent stability toward acid, base, high temperature, and photo-irradiation. The facile synthesis, excellent stability, strong and tunable fluorescence emission make BTAB interesting new fluorescent probes for future chemical and biological applications.
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- Award ID(s):
- 2054180
- NSF-PAR ID:
- 10348836
- Date Published:
- Journal Name:
- Chemical Science
- Volume:
- 13
- Issue:
- 20
- ISSN:
- 2041-6520
- Page Range / eLocation ID:
- 5982 to 5987
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Density functional theory has been used to elucidate the mechanistic underpinnings of the regeneration of ammonia‐borane (H3B−NH3,
AB ) from polyborazylene (BxNxHx,PBz ) in the presence of hydrazine (H2N−NH2,Hz ). Herein, borazine (B3N3H6,Bz ) is used as the simplest relevant model ofPBz for the regeneration process. Digestion ofBz usingHz was found to occur by a string of Lewis acid base adduct (between B atoms ofBz andHz molecule) formation andHz assisted proton transfer processes. Later, B−H bonds of HB(NHNH2)2, theBz digested product, are redistributed to form hydrazine‐borane (H3B−NH2NH2,HzB ) and B(NHNH2)3. Redistribution of B−H bonds occurs through hydroboration and concerted proton‐hydride transfer. Another B−H redistributed product, B(NHNH2)3, producesHzB as a result of proton and hydride transfer from cis‐diazene (Dz ), the oxidized product ofHz in presence of O2. -
The tetramer of bis(4-di- n -butylaminophenyl)(pyridin-3-yl)borane [systematic name: 2λ 4 ,4λ 4 ,6λ 4 ,8λ 4 -tetrabora-1,3,5,7(1,3)-tetrapyridinacyclooctaphane-1 1 ,3 1 ,5 1 ,7 1 -tetrakis(ylium)], C 132 H 192 B 4 N 12 , was synthesized unexpectedly and crystallized. Its structure contains an unusual 16-membered ring core made up of four (pyridin-3-yl)borane groups. The ring adopts a conformation with pseudo- S 4 symmetry that is very different from the two other reported examples of this ring system. Density functional theory (DFT) computations indicate that the stability of the three reported ring conformations is dependent on the substituents on the B atoms, and that the pseudo- S 4 geometry observed in the bis(4-dibutylaminophenyl)(pyridin-3-yl)borane tetramer becomes significantly more stable when phenyl or 2,6-dimethylphenyl groups are attached to the boron centers.more » « less
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Abstract We report hydroboration of carbodiimide and isocyanate substrates catalyzed by a cyclic carbodiphosphorane catalyst. The cyclic carbodiphosphorane outperformed the other Lewis basic carbon species tested, including other zerovalent carbon compounds, phosphorus ylides, an
N ‐heterocyclic carbene, and anN ‐heterocyclic olefin. Hydroborations of seven carbodiimides and nine isocyanates were performed at room temperature to formN ‐boryl formamidine andN ‐boryl formamide products. Intermolecular competition experiments demonstrated the selective hydroboration of alkyl isocyanates over carbodiimide and ketone substrates. DFT calculations support a proposed mechanism involving activation of pinacolborane by the carbodiphosphorane catalyst, followed by hydride transfer and B−N bond formation. -
Abstract Recent years have witnessed marked progress in the efficient synthesis of various enantioenriched 1,2,3,4-tetrahydroquinoxalines. However, enantio- and diastereoselective access to trans-2,3-disubstituted 1,2,3,4-tetrahydroquinoxalines remains much less explored. Herein we report that a frustrated Lewis pair-based catalyst generated via in situ hydroboration of 2-vinylnaphthalene with HB(C6F5)2 allows for the one-pot tandem cyclization/hydrosilylation of 1,2-diaminobenzenes and 1,2-diketones with commercially available PhSiH3 to exclusively afford trans-2,3-disubstituted 1,2,3,4-tetrahydroquinoxalines in high yields with excellent diastereoselectivities (>20 : 1 dr). Furthermore, this reaction can be rendered asymmetric by using an enantioenriched borane-based catalyst derived from HB(C6F5)2 and a binaphthyl-based chiral diene to give rise to enantioenriched trans-2,3-disubstituted 1,2,3,4-tetrahydroquinoxalines in high yields with almost complete diastereo- and enantiocontrol (>20 : 1 dr, up to >99 % ee). A wide substrate scope, good tolerance of diverse functionality and up to 20-gram scale production are demonstrated. The enantio- and diastereocontrol are achieved by the judicious choice of borane catalyst and hydrosilane. The catalytic pathway and the origin of the excellent stereoselectivity are elucidated by mechanistic experiments and DFT calculations.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D2SC01103D
