A Versatile Route to 3-Benzoheteroepines Containing Group 15 and 16 Heavier Elements Involving Several Novel Ring Systems, and Their Thermal Stabilities

Yasuike, Shuji; Kiharada, Tsutomu; Tsuchiya, Takashi; Kurita, Jyoji

doi:10.1248/cpb.51.1283

Cited by 24 publications

(19 citation statements)

References 36 publications

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“…Illustrative is the condensation of 5 with PhPH 2 -Mn(CO) 2 Cp that gives manganese-complexed phosphepine 7b (35%). The molecule in the crystal shows again C s -symmetry, but has a flatter phosphepine ring with a dihedral angle of 34.49 (8)°b etween the C1-P1-C1i and hydrocarbon planes (Figure 2). This is best explained by a steric effect of the Cp, hanging over the phosphepine ring, in which CdC bond alternation is again evident.…”

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“…12 The more shielded 31 P NMR resonance at +64 ppm points to less electrophilic character for the phosphorus group than in 7a; the 1 H and 13 C NMR parameters are similar, including the 2 J HP (20.7 Hz) and 3 J HP (32.1 Hz) coupling constants. Phosphepines 8 and 9 are known to decompose readily to the aromatic hydrocarbon and (RP) 5 , presumably by expelling [RP] from the NCD intermediates 7,8 (Chart 1). Interestingly, in the case of complex 7 this would result in the expulsion of a transition metalstabilized phosphinidene [R-PdML n ].…”

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Phosphepines: Convenient Access to Phosphinidene Complexes

et al. 2005

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The cycloheptatriene-norcaradiene (CHT-NCD) equilibrium exemplifies a 6-el electrocyclic reaction with a modest barrier separating the valence tautomers 1C and 2C. 1 Less is known about the heterocyclic analogues (X ) O, S, NR, PR) (Scheme 1). For those with an oxygen atom, benzene oxide 2O is the more stable form, but entropy factors shift the equilibrium toward oxepin 1O at room temperature. 2 Only the monocyclic form is observed for thiepins 3 1S and 1H-azepines 4 1N, and both require bulky groups and/or extended conjugation for stability. Of the phosphorus analogue, phosphepine 1P, only its oxide 5 and 2,7-dialkylsubstituted 6 and annelated 7,8 derivatives are known, but without structural details. Here we describe a computational analysis of the 1P-2P equilibrium and present new stable phosphepine derivatives and a novel application.Phosphepines equilibrate with phosphanorcaradienes (benzene phosphines) such as CHT with NCD. DFT calculations for the parent system give an energetic preference for NCD 2P over CHT 1P (∆E 2-1 -4.2 kcal/mol, Table 1) with a modest 1P f 2P barrier (10.6 kcal/mol), reflecting the same behavior as the thia analogues (∆E 2-1 -7.8 (S) kcal/mol). A 1,5-sigmatropic shift relates NCD 2P with the 15.5 kcal/mol less stable 7-phosphanorbornadiene 3P, neither of which is known experimentally, except for a strained derivative of 3P, 10 presumably due to release of the phosphorus group to give pentamers, (PR) 5 .Transition metal coordination at phosphorus stabilizes 1P over 2P because the distal C-C bond is weakened by σ,π-interactions (Scheme 2), reversing the order for W(CO) 5 (∆E 2-1 1.5 kcal/mol). Due to extended conjugation, benzannelation has an even stronger influence, reversing the CHT-NCD equilibrium in favor of 1P by 11.0 kcal/mol. These cumulative electronic effects give a 16.8 kcal/mol energetic preference of benzophosphepine W(CO) 5 complex over its valence isomer 2P with a 24.7 kcal/mol barrier for electrocyclization. 11 On the basis of these calculations benzophosphepine complexes 7 are expected to be stable at room temperature. Indeed, 7 could be synthesized from the complexed phosphine and 1,2-diethynylbenzene (5) by a modified Märkl's procedure 7 (Scheme 3). Dialkyne 5 was obtained in 91% yield from commercially available o-phthaldialdehyde (4) by a one-carbon homologation-oxidation sequence. The base-promoted double hydrophosphination of 5 with PH 2 Ph-W(CO) 5 (6a) gave 3H-3-benzophosphepine-W(CO) 5 7a in 74% yield as yellow crystals. W(CO) 5 coordination causes shielding of the 31 P NMR resonance (δ -15 vs -33 ppm), shielding of the C1,C5 13 C NMR resonances (by 6 ppm), and reduces the 2 J CP coupling constants (1.6 vs 21.1 Hz). 7 Distinctive are the coupling constants for the olefinic protons with a sizable 3 J HH (12.4 Hz) and with a 3 J HP (33.4 Hz) being much larger than the 2 J HP (21.3 Hz).The crystal structure (C s -symmetry) shows alternating CdC bonds (no homoaromaticity) for the boat-shaped phosphepine ring (Figure 1) that has the phosphorus atom shifted out of t...

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Phosphepines: Convenient Access to Phosphinidene Complexes

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“…Notably, the mass spectrum of 2,7-di-tert-butylthiepine does not show ions generated by the loss of sulfur, an observation that is unexpected. [82] Tautomerism in azepines via an allowed 1,5-hydrogen shift has been studied for different azepine isomers and it was found that the ratio of azepine tautomers is related to their relative thermal stabilities [69d, 86]. For instance, when heated in toluene both 2H-and 3H-azepines 2 and 3 are converted into mixtures containing the 2H-, 3H-, and 4H-azepine tautomers in similar ratio (about 10: 50: 1).…”

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“…However, 3-benzothiepine (20) has been prepared from phthalaldehyde [224] under the conditions shown in Scheme 21.62.…”

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Seven‐Membered Heterocycles: Azepines, Benzo Derivatives and Related Systems

Vaquero

Cuadro

Herradón

2011

Modern Heterocyclic Chemistry

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The replacement of a carbon atom by a heteroatom in a seven-membered carbocycle leads to the corresponding seven-membered heterocyclic ring system. Different types of heterocycles can be formed depending on the nature of the carbocycle. In a cycloheptatriene the replacement can involve any of the six sp 2 hybridized carbons or the sp 3 carbon atom, whereas in cycloheptane all carbon atoms are equivalent and replacement affords exclusively the fully saturated heterocyclic systems. Partially saturated seven-membered heterocycles can be viewed as derivatives or related systems of these two main seven-membered heterocyclic units arising from carbon replacement in cycloheptatriene and in cycloheptane. Replacement of the sp 3 hybridized carbon atom in cycloheptatriene by a nitrogen leads to an azacycloheptatriene known as 1H-azepine (1) and the corresponding 2H-, 3H-, and 4H-azepines (2-4) are the tautomeric forms generated by the replacement of the sp 2 carbons. 1H-Azepine is an unstable red oil that is prone to rearrange to the also unstable 3H-azepine in the presence of acids and bases. However, this tautomer seems to be more stable than both 4H-and 2H-azepine. The structures related to 1H-azepine that bear an oxygen or sulfur atom are known as oxepine (5) and thiepine (6) (thiepin is favored by Chemical Abstracts Service). Oxepine is much more stable than thiepine and has been synthesized, isolated, and characterized at room temperature while thiepine has not been detected to date. Stable monocyclic thiepines were prepared and characterized in the 1980s. Azepines, oxepines, and thiepines that are constrained to planar or almost planar conformations should be antiaromatic molecules with negative resonance energy and, as a consequence, these compounds are unknown.The fully saturated seven-membered heterocycle containing one nitrogen is azepane (7) (hexahydroazepine or perhydroazepine); the oxygen and sulfur analogues are known as oxepane (8) and thiepane (9). All of these compounds are stable and show typical behavior of secondary amine, ether and thioether, respectively. TwoModern Heterocyclic Chemistry, First Edition. Edited

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Cyclic Hydrocarbon Frameworks Containing Two Bismuth Atoms: Towards 9,10‐Dibismaanthracene

Rottschäfer,

Reith,

Schwarzmann

et al. 2024

Chemistry A European J

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When bismuth atoms are incorporated into cyclic organic systems, this commonly goes along with strained or distorted molecular geometries, which can be exploited to modulate the physical and chemical properties of these compounds. In sixmembered heterocycles, bismuth atoms are often accompanied by oxygen, sulfur or nitrogen as a second hetero‐element. In this work, we present the first examples of six‐membered rings, in which two CH units are replaced by BiX moieties (X = Cl, Br, I), resulting in dihydroanthracene analogs. Their behavior in chemically reversible reduction reactions is explored, aiming at the generation of dibismaanthracene (bismanthrene). Heterometallic compounds (Bi/Fe, Bi/Mn) are introduced as potential bismanthrene surrogates, as supported by bismanthrene‐transfer to selenium. Analytical techniques used to investigate the reported compounds include NMR spectroscopy, highresolution mass spectrometry, single‐crystal X‐ray diffraction analyses, and DFT calculations.

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A Versatile Route to 3-Benzoheteroepines Containing Group 15 and 16 Heavier Elements Involving Several Novel Ring Systems, and Their Thermal Stabilities

Cited by 24 publications

References 36 publications

Phosphepines: Convenient Access to Phosphinidene Complexes

Phosphepines: Convenient Access to Phosphinidene Complexes

Seven‐Membered Heterocycles: Azepines, Benzo Derivatives and Related Systems

Cyclic Hydrocarbon Frameworks Containing Two Bismuth Atoms: Towards 9,10‐Dibismaanthracene

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