The syntheses and conformational studies of [n](2,4)heterophanes and [7](3,5)pyrazolophane

Hirano, S.; Hiyama, Tamejiro; Fujita, Shinsaku; Kawaguti, Takeyuki; Hayashi, Yukiko; Nozaki, Hitosi

doi:10.1016/s0040-4020(01)97422-8

Cited by 31 publications

(8 citation statements)

References 21 publications

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“…In this study (Table ), 3-methylenecyclodecanone ( 3 , n = 6) isomerized to two 2-cyclodecenone isomers at similar rates (Figure ), but only one of these isomers was present after 2 weeks under the isomerization conditions at 80 °C. This more stable product was assigned the Z structure on the basis of comparison with previous results and on spectral data (infrared comparison with the spectrum reported for the unsubstituted ( Z )-2-cyclodecenone by Whitham 4 and by Hirano, a more upfield shift in the NMR for the methyl hydrogens than in the other isomer, comparison with the spectra of Still's 10-methyl-2-cyclodecenones, and comparison with all spectral data for the 8- and 9-membered ring analogues, which must be Z ). Only one 3-methyl-3-cyclodecenone was obtained in these isomerization studies, and it is assigned the Z configuration by spectral comparison with its smaller ring analogues.…”

Section: Isomerizationsmentioning

confidence: 66%

“…Assignment of the Z configuration is based upon stability considerations, comparison of spectral data with the smaller rings in the series ( all-Z ), and with a similar dehydromuscone and related materials. ,, …”

Section: Methodsmentioning

confidence: 99%

“…When this synthetic scheme was virtually complete, a synthesis of 3-methylenecycloheptanone ( 3 , n = 3) from 2-cycloheptenone was published − of obtaining the analogous enones in high yield. …”

Section: Synthesismentioning

confidence: 99%

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Medium-Ring Systems. 6.¹ Synthesis and Isomerizations of Medium-Ring 3-Methylenecycloalkanones and 3-Methylcycloalkenones

Eskola

Hirsch

1997

J. Org. Chem.

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A series of 3-methylenecycloalkanones with ring sizes 7−10 has been prepared and subjected to base-catalyzed isomerization. Equilibrium between these exocyclic isomers and the corresponding 3-methyl-2-cycloalkenones and 3-methyl-3-cycloalkenones was reached in the 7- and 8-membered rings. The presence of the β-methyl shifts these equilibria toward the Δ2 isomer in each ring relative to the unsubstituted compounds and to compounds containing electron-withdrawing groups at the β position. In the 9- and 10-membered rings, the Δ2 isomers were isomerized to the Δ3 isomers only with difficulty, and the reverse process could not be accomplished under the reaction conditions utilized. The ease of interconversion of the Δ2 and Δ3 isomers is directly related to the thermodynamic stability of planar conjugated dienes in medium ring carbocycles.

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Section: Isomerizationsmentioning

confidence: 66%

Section: Methodsmentioning

confidence: 99%

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Medium-Ring Systems. 6.¹ Synthesis and Isomerizations of Medium-Ring 3-Methylenecycloalkanones and 3-Methylcycloalkenones

Eskola

Hirsch

1997

J. Org. Chem.

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“…(162) The ö-tolyl compound is essentially rigid up to 150°, due to steric interaction between the ö-methyl group and the alkane bridge, but the aryl rings of the phenyl and /?-tolyl derivatives rotate freely at room temperature having a rotational energy barrier of only ca. The energy barrier to inversion has been estimated to be >97 kJ mol~1 (167) (cf. (162) The NMR spectrum of N,7V'-/?-phenylene di [8](2,5)pyrrolophane (D3) (R = H) varies with temperature.…”

Section: DLmentioning

confidence: 99%

Alkylpyrroles and Related Compounds

1977

The Chemistry of Pyrroles

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“…The ready accessibility of ketones 3 and 7 via simple and inexpensive procedures [4][5][6] prompted their selection as suitable substrates. When initial attempts to achieve their direct α -iodination 7 were seriously complicated by competing attack at the α ' position, we became all the more interested in being able to control the regiochemistry in these systems.…”

mentioning

confidence: 99%

Synthetic Studies Involving Bridgehead α,β-Unsaturated Ketones: Protocols for Regiocontrolled α-Methylation

Paquette¹,

Wang²,

Zhuang³

1998

Synthesis

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Bicyclo[5.3.1]undec-10-en-9-one ( 3 ) has been converted via two routes into the 10-methyl homolog 11 . The first pathway consists of α -phenylthiomethylation and subsequent desulfurization with Raney nickel. The second sequence proceeds via the 1,2-addition of ethylmagnesium bromide followed by dihydroxylation, ring cleavage with lead tetraacetate, and basepromoted cyclization.The diterpenoid class of natural products defined by the taxanes, encompassing many members, constitutes a challenging area of targeted total synthesis as a consequence of the structural complexity and biomedical importance of select members. 1 Previous accounts from this laboratory have dealt with the design and development of a unique strategy that assembles virtually all of the essential structural features inherent in taxusin 2 and taxol 3 with the utmost brevity. Our projected end game involves ultimate installation of the C-18 methyl substituent resident on the A-ring as expediently as possible. The need to convert 1 into 2 illustrates the problem. This fundamental transformation does not surface in other approaches, but is mandated in our route because the A-ring is crafted from D-camphor whose absolute configuration is ideally matched with that of the taxanes.Herein, various methods are evaluated for their capability to accomplish the indicated synthetic objective in the context of model bridgehead enones. As a consequence of the unusual structural setting of the double bond, the reactivity of two differently strained candidates was compared.In certain settings, this variation in torsional stress was reflected in noteworthy reactivity differences. In the final analysis, two distinctively different schemes were found to be uniquely qualified for more advanced deployment in the more sterically congested environments resident in 1 and its congeners.The ready accessibility of ketones 3 and 7 via simple and inexpensive procedures 4-6 prompted their selection as suitable substrates. When initial attempts to achieve their direct α -iodination 7 were seriously complicated by competing attack at the α ' position, we became all the more interested in being able to control the regiochemistry in these systems. These concerns were exacerbated by subsequent recognition of the fact that, whereas 3 smoothly underwent 1,4-addition in the presence of Me 2 AlSPh 8 to provide 4 (Scheme 1), subsequent methylation of this functionalized ketone led only to the undesired product 5 . DBU-induced elimination 9 within 5 provided 6 in good yield. Attempts to trap the aluminum enolate that mediates the conversion of 3 into 4 was to no avail, this species being quite unreactive even in neat HMPA. Adaptation of the latter conditions afforded 5 in 50% yield alongside the elimination products 3 (18%) and 6 (17%). These events signaled that reintroduction of the double bond would not be problematical.Subsequently investigated was the possibility that α -phenylthiomethylation would operate as in more conventional cyclohex-2-enones. 10 As shown in Scheme 2, 7 is ent...

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The syntheses and conformational studies of [n](2,4)heterophanes and [7](3,5)pyrazolophane

Cited by 31 publications

References 21 publications

Medium-Ring Systems. 6.¹ Synthesis and Isomerizations of Medium-Ring 3-Methylenecycloalkanones and 3-Methylcycloalkenones

Medium-Ring Systems. 6.¹ Synthesis and Isomerizations of Medium-Ring 3-Methylenecycloalkanones and 3-Methylcycloalkenones

Alkylpyrroles and Related Compounds

Synthetic Studies Involving Bridgehead α,β-Unsaturated Ketones: Protocols for Regiocontrolled α-Methylation

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The syntheses and conformational studies of [n](2,4)heterophanes and [7](3,5)pyrazolophane

Cited by 31 publications

References 21 publications

Medium-Ring Systems. 6.1 Synthesis and Isomerizations of Medium-Ring 3-Methylenecycloalkanones and 3-Methylcycloalkenones

Medium-Ring Systems. 6.1 Synthesis and Isomerizations of Medium-Ring 3-Methylenecycloalkanones and 3-Methylcycloalkenones

Alkylpyrroles and Related Compounds

Synthetic Studies Involving Bridgehead α,β-Unsaturated Ketones: Protocols for Regiocontrolled α-Methylation

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Medium-Ring Systems. 6.¹ Synthesis and Isomerizations of Medium-Ring 3-Methylenecycloalkanones and 3-Methylcycloalkenones

Medium-Ring Systems. 6.¹ Synthesis and Isomerizations of Medium-Ring 3-Methylenecycloalkanones and 3-Methylcycloalkenones