Benzannelated annulenes. 7. Toward the understanding of benzannelated annulenes: synthesis and properties of an [e]-ring monobenzannelated dihydropyrene

Mitchell, Reginald H.; YAN, J. S. H.; Dingle, Thomas W.

doi:10.1021/ja00373a037

Cited by 40 publications

(30 citation statements)

References 5 publications

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“…There was no detectable quantity of the corresponding syn isomer 27b . The anti stereochemistry of 27a was confirmed by its significantly shielded internal methyl protons at δ 0.87 similar to that reported for anti 28 (δ 0.94) …”

Section: Resultssupporting

confidence: 75%

“…(a) Synthesis. The synthesis of [ e ]-ring annelated derivatives of 11 commonly involves, as a precursor, a suitably substituted tert -aryl derived from an o -dibromo aromatic compound or an o -quinone. 10b,− These approaches are, however, inappropriate for the synthesis of a 3,4-diarylfuran. In order to minimize any complication from addition and/or substitution reactions at the 2,5-positions of a furan ring, we have selected the 3,4-diarylfuran 16 as a synthetic precursor for 15b .…”

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

Synthesis and Diatropicity of trans-2‘,5‘,10b,10c-Tetramethylfurano[3,4-e]-10b,10c-dihydropyrene. A Valence Isomerization To Form a Novel Isoannulenofuran at the Expense of Two Benzene and One Furan Rings

Lai

Chen

1996

J. Org. Chem.

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The 1,4-dicarbonyl compound 22 was prepared by an oxidative coupling of the benzyl methyl ketone 19. Dehydration of 22 gave the 3,4-diarylfuran 16 which upon functional group transformations and a subsequent intramolecular cyclization afforded only the anti isomer of the furanothiacyclophane 27. Ring contraction following a Wittig rearrangement−Hofmann elimination sequence led to the isolation of anti furanocyclophanene 15b. Valence isomerization of 15b to the isoannulenofuran 14b could be achieved either photochemically or thermally with 15b as the thermodynamically more stable isomer. Compound 14b was found to exhibit only a very small ring current. The diatropicity of 14b is clearly affected by a weak participation of the oxygen in π-electron delocalization and a steric effect of its external methyl groups resulting in a deviation from planarity of its molecular periphery. The thermal conversion of 15b to 14b was determined to have a high activation energy of 114 kJ mol-1. This thermal process, in addition to involving the disruption of π-electron delocalization in two benzene and one furan rings, is another example of an unsual concerted, symmetry-forbidden reaction.

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Section: Resultssupporting

confidence: 75%

Section: Resultsmentioning

confidence: 99%

Synthesis and Diatropicity of trans-2‘,5‘,10b,10c-Tetramethylfurano[3,4-e]-10b,10c-dihydropyrene. A Valence Isomerization To Form a Novel Isoannulenofuran at the Expense of Two Benzene and One Furan Rings

Lai

Chen

1996

J. Org. Chem.

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“…The explanation is given in the 1990 paper, 63 and principally rests on looking at the relative resonances of the annulene vs. the annulated moiety. In a series of papers, [64][65][66][67][68] Mitchell showed that when a benzene is annulated (3 and 4), the chemical shift of the central H and Me is shifted downfield by 4.14 and 2.65 ppm, respectively, for 3, and by 2.4 ppm for 4. For 5 and 6, it was found that the chemical shift of the central Me groups is 0.02 and À3.58 ppm, respectively.…”

Section: Nmrmentioning

confidence: 99%

Magnetic criteria of aromaticity

2015

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This review describes the current state of magnetic criteria of aromaticity. The introduction contains the fundamentals of ring currents in aromatic and antiaromatic systems, followed by a brief description of experimental and computational tools: NMR, diamagnetic susceptibility exaltation, current density analyses (CDA) and nucleus independent chemical shifts (NICS). This is followed by more comprehensive chapters: NMR - focusing on the work of R. Mitchell - NICS and CDA - describing the progress and development of the methods to their current state and presenting some examples of representative work.

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“…NBS can also be used in CHCl 3 or CH 2 Cl 2 could be accessed. [18,26,27] Still however, using the dhp now as the starting material for another long sequence was a and with 39 can be controlled [32] to yield either the mono-(40) or dibromide (41, Scheme 8). Reaction of 40 with daunting prospect for many new students!…”

Section: Synthesesmentioning

confidence: 99%

“…Bodwell [14] has recently obtained a tethered cis-di-light. Irradiation with UV light quantitatively returns 24. hydropyrene 19, which exists in equilibrium with the syn-Thermally, diene 23 also returns to dihydropyrene (dhp) 24. cyclophanediene 20, but it remains to be seen how revers-E act for this thermal reaction is 25 kcal/mol [18] compared to ible this isomerization is. In 1981 [15] we made the diene 21. the 23 kcal/mol found for the parent 8.…”

mentioning

confidence: 99%