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Torquoselective ring opening of fused cyclobutenamides: evidence for a cis,trans-cyclooctadienone intermediate.

Wang XN, Krenske EH, Johnston RC, Houk KN, Hsung RP - J. Am. Chem. Soc. (2014)

Bottom Line: Electrocyclic ring opening of 4,6-fused cyclobutenamides 1 under thermal conditions leads to cis,trans-cyclooctadienones 2-E,E as transient intermediates, en route to 5,5-bicyclic products 3.Theoretical calculations predict that 4,5-fused cyclobutenamides should likewise undergo thermal ring opening, giving cis,trans-cycloheptadienones, but in this case conversion to 5,4-bicyclic products is thermodynamically disfavored, and these cyclobutenamides instead rearrange to vinyl cyclopentenones.

View Article: PubMed Central - PubMed

Affiliation: Division of Pharmaceutical Sciences and Department of Chemistry, University of Wisconsin , Madison, Wisconsin 53705, United States.

ABSTRACT
Electrocyclic ring opening of 4,6-fused cyclobutenamides 1 under thermal conditions leads to cis,trans-cyclooctadienones 2-E,E as transient intermediates, en route to 5,5-bicyclic products 3. Theoretical calculations predict that 4,5-fused cyclobutenamides should likewise undergo thermal ring opening, giving cis,trans-cycloheptadienones, but in this case conversion to 5,4-bicyclic products is thermodynamically disfavored, and these cyclobutenamides instead rearrange to vinyl cyclopentenones.

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Structurally diverseproducts accessed through thermal rearrangementsof cyclobutenamides 1.
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fig1: Structurally diverseproducts accessed through thermal rearrangementsof cyclobutenamides 1.

Mentions: The scope and generality of this fascinatingcascade are accentuatedin Figure 1. Variation of substituents on thenitrogen atom and/or the β-carbon of the starting cyclobutenamidesled to the pentalanes 3d (Table 1) and 3e–h (Figure 1). The initially formed hydroxypentalanes could undergo syn-dehydration to fulvenes, which may be isolated (3e′ and 3f′) or trapped by an intramolecular[4 + 2] cycloaddition onto a tethered alkene to give tetracycles (3h″ and 3g″). These last two examplesreveal the synthetic potential of this rearrangement for the rapidassembly of structural complexity. It is also noteworthy that, inthe case of 3e/3e′, only the Z exocyclic olefin was found.


Torquoselective ring opening of fused cyclobutenamides: evidence for a cis,trans-cyclooctadienone intermediate.

Wang XN, Krenske EH, Johnston RC, Houk KN, Hsung RP - J. Am. Chem. Soc. (2014)

Structurally diverseproducts accessed through thermal rearrangementsof cyclobutenamides 1.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4353010&req=5

fig1: Structurally diverseproducts accessed through thermal rearrangementsof cyclobutenamides 1.
Mentions: The scope and generality of this fascinatingcascade are accentuatedin Figure 1. Variation of substituents on thenitrogen atom and/or the β-carbon of the starting cyclobutenamidesled to the pentalanes 3d (Table 1) and 3e–h (Figure 1). The initially formed hydroxypentalanes could undergo syn-dehydration to fulvenes, which may be isolated (3e′ and 3f′) or trapped by an intramolecular[4 + 2] cycloaddition onto a tethered alkene to give tetracycles (3h″ and 3g″). These last two examplesreveal the synthetic potential of this rearrangement for the rapidassembly of structural complexity. It is also noteworthy that, inthe case of 3e/3e′, only the Z exocyclic olefin was found.

Bottom Line: Electrocyclic ring opening of 4,6-fused cyclobutenamides 1 under thermal conditions leads to cis,trans-cyclooctadienones 2-E,E as transient intermediates, en route to 5,5-bicyclic products 3.Theoretical calculations predict that 4,5-fused cyclobutenamides should likewise undergo thermal ring opening, giving cis,trans-cycloheptadienones, but in this case conversion to 5,4-bicyclic products is thermodynamically disfavored, and these cyclobutenamides instead rearrange to vinyl cyclopentenones.

View Article: PubMed Central - PubMed

Affiliation: Division of Pharmaceutical Sciences and Department of Chemistry, University of Wisconsin , Madison, Wisconsin 53705, United States.

ABSTRACT
Electrocyclic ring opening of 4,6-fused cyclobutenamides 1 under thermal conditions leads to cis,trans-cyclooctadienones 2-E,E as transient intermediates, en route to 5,5-bicyclic products 3. Theoretical calculations predict that 4,5-fused cyclobutenamides should likewise undergo thermal ring opening, giving cis,trans-cycloheptadienones, but in this case conversion to 5,4-bicyclic products is thermodynamically disfavored, and these cyclobutenamides instead rearrange to vinyl cyclopentenones.

Show MeSH