1,2‐Phosphaborines: Hybrid Inorganic/Organic P–B Analogues of Benzene

Barnard, Jonathan H.; Brown, Paul A.; Shuford, Kevin L.; Martin, Caleb D.

doi:10.1002/anie.201507003

Cited by 67 publications

(58 citation statements)

References 75 publications

(11 reference statements)

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“…The reactivity of boroles 1 and 20 with diazoalkanes, much like azides, proved to be dependent on the steric bulk of the substituents, in this case, on the α--carbon atom of the diazoalkane (Fig 10). 57 The PBC 4 ring is highly planar with C--C and C--B bond lengths intermediate between single and double bonds, consistent with those reported for 1,2--azaborines. The bulkier di-tolyl--substituted derivative resulted in insertion of the terminal nitrogen to form 1,2--azaborines 24 and 25 akin to the conversion of Int15 to 23 in the azide mechanism.…”

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Ring expansion reactions of anti-aromatic boroles: a promising synthetic avenue to unsaturated boracycles

et al. 2016

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Conjugated boron heterocycles have emerged as attractive synthetic targets due to their potential in medicinal chemistry and as electronic materials. However, the development of unsaturated boracycles has been hampered by difficulties in their preparation. Recently, a new synthetic avenue to access these species has been developed that takes advantage of the high reactivity of boroles. These five-membered anti-aromatic heterocycles can react with substrates to furnish ring expansion products via the insertion of one, two, or three atoms into the boracyclic ring. The ring expansion can occur via two pathways, the first exploits the activated diene moiety of the heterocycle in Diels-Alder chemistry with the resulting bicyclic species undergoing further rearrangements. The second reaction pathway is initiated by the coordination of the Lewis basic site of a substrate to the highly Lewis acidic boron center rendering the endocyclic B-C bond of the borole nucleophilic, inducing the formation of larger boracycles via attack at the electrophilic site of the substrate. This review summarizes the current state of this chemistry and details the mechanisms leading to the products. The methodologies described herein could very well be extended to other substrates, as well as applied to other anti-aromatic heterocycles.

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confidence: 83%

Ring expansion reactions of anti-aromatic boroles: a promising synthetic avenue to unsaturated boracycles

et al. 2016

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“…As indicated by the sums of the bond angles about B1 and N1 of 360.0° and 359.9°, respectively, the heteroatoms adopt almost perfectly trigonal‐planar coordination geometries. The molecular structure of 9 could also be obtained, but a disorder in the heterocycle, which is frequently encountered for these types of structures, prevented a more accurate analysis of the metric parameters. Nevertheless, it is interesting to note that all aryl substituents, including the thienyl group on boron, are arranged in a propeller‐like fashion around the central ring, indicating no significant conjugation between them .…”

Section: Resultsmentioning

confidence: 99%

Scope of the Thermal Ring‐Expansion Reaction of Boroles with Organoazides

Braunschweig

Çelik

Dellermann

et al. 2017

Chemistry A European J

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Electronic and steric factors have been investigated in the thermalr ing expansion of borolesw ith organic azides,areaction that providesa ccess to highly arylated 1,2-azaborinines,BNanalogues of benzene.Reactions of avariety of boroles and organic azides demonstrate that the synthetic methodi sq uite generali nf urnishing 1,2-azaborinines,b ut the respective reaction rates reveal as trongd ependence on the substituents on the two reactants. The productsh ave been characterizedb yU V/Vis, electrochemical, NMR, and Xray diffractionm ethods, clarifying their constitutions and highlighting substituent effects on the electronic structure of the 1,2-azaborinines. Furthermore, analysiso fs everalp ossible mechanistic pathways for 1,2-azaborinine formation,a s studied by DFT,r evealed that at wo-step mechanism involving azide-borole adduct formation and nitrene insertion is favored.

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“…With respect to boron–oxygen analogues (1,2‐oxaborines, B ), numerous fused polycyclic systems are known, as well as five monocyclic species . Fewer advances have been made for the third row; in fact, the first 1,2‐phosphaborine C was reported only last year . For sulfur, the reported derivatives are limited to two fused polycyclic systems, specifically phenanthrene analogues ( 1 and 2 ) and only a singular example of a 1,2‐thiaborine exists, reported by Ashe ( 3 ) .…”

Section: Figurementioning

confidence: 99%