Synthesen in der hydroaromatischen Reihe. VI. Die Addition von 1‐Vinyl‐6‐methoxy‐3,4‐dihydro‐naphtalin an Δ<sub>1</sub>‐Cyclopentenon und an Δ<sub>1</sub>‐4,4′‐Dibrom‐cyclopenten‐dion‐3,5

Dane, Elisabeth; Eder, Kurt

doi:10.1002/jlac.19395390117

Cited by 32 publications

(7 citation statements)

References 6 publications

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“…About 60 years ago, the Diels−Alder reaction of diene 1 and diketone 2a (Scheme ) was investigated in the hope of finding, via the intermediate rac- 5a , the first synthetic route toward estrone . The noncatalyzed cycloaddition, however, has a strong preference for the constitutional isomer rac- 6a , thus preventing successful synthesis in those days .…”

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confidence: 99%

Axially Chiral Amidinium Ions as Inducers of Enantioselectivity in Diels−Alder Reactions

et al. 2000

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[reaction: see text] Enantioselective catalysis of Diels-Alder reactions is mostly achieved by coordinating the dienophile to relatively strong chiral Lewis acids. Here we report on a novel approach employing the hydrogen-bond-mediated association of dienophiles to chiral host molecules. In a reaction forming the steroid skeleton of norgestrel, chiral amidinium ions induce 5:ent-5 ratios of up to 2.5:1. Improved and simplified amidinium catalysts may become interesting candidates to perform stereoselective transformations.

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confidence: 99%

Axially Chiral Amidinium Ions as Inducers of Enantioselectivity in Diels−Alder Reactions

et al. 2000

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“…Clearly, 28 resulted from double-bond isomerization of the primary DA product 27. This type of acid-induced isomerization is well precedented in earlier Dane's-diene-based routes to steroids (39)(40)(41)(42)(43). It should be noted that when conducted thermally, DA reactions of cyclenones with 26 are not significantly regioselective (44,45).…”

Section: Significancementioning

confidence: 99%

Stereospecific cis- and trans -ring fusions arising from common intermediates

Townsend

Ross

2014

Proc. Natl. Acad. Sci. U.S.A.

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Highly concise and stereospecific routes to cis and trans fusion, carrying various functionality at one of the bridgehead carbons, have been accomplished. Diels-Alder cycloaddition | cyclobutenone | angular methylation | mechanistic studies O ur group has been studying the synthetic utility of the DielsAlder (DA) reaction of the parent cyclobutenone, 2 (1). Recently reported results demonstrate that 2 is a highly reactive, endo-selective dienophile (Fig. 1, Eq. 1) (2). We have also developed a series of intramolecular Diels-Alder (IMDA) reactions, wherein the cyclobutenone component is tethered to various conjugated dienes (compare 4); cycloaddition of these substrates delivers adducts of the type 5, which can be readily converted to trans-fused systems bearing iso-DA patterns (Fig. 1, Eq. 2, 5→6) (3). Additionally, we have described the synthesis and DA cycloaddition of an even more powerful dienophile, 2-bromocyclobutenone (Fig. 1, Eq. 3, 7) (4). The direct adducts of this [4+2] reaction (compare 8) are readily converted to norcarane carboxylic acids (9) through exposure to hydroxide base. The research described herein was initially focused on efforts to add carbon-based nucleophiles to DA cycloadducts of the type 8. It might well have been expected that such reactions would give rise to products such as 10, wherein a ketone is appended to the junction of the norcarane system (Fig. 1, Eq. 4). Results and DiscussionWith a view toward accomplishing the transformation envisioned in Fig. 1, Eq. 4, compounds of the type 8 were exposed to methyllithium as described in Fig. 2. Interestingly, exposure of substrate 8a to the conditions shown led to an 81% yield of the angularly methylated product 11a, apparently unaccompanied by any part of the corresponding trans-fused diastereomer (Fig. 2, entry 1). Reactions conducted with related DA adducts 8b and 8c resulted in quite similar outcomes (Fig. 2, entries 2 and 3). Although we were confident that the products obtained were cisfused (Fig. 2, 11a-c), it was the synthesis of the rigorously assignable trans-fused product (vide infra) and its nonidentity with 11a that served to allow for sound assignment of the cisring fusion.An obvious mechanistic proposal to account for the formation of this structure envisions lithium-halogen exchange (5-8) leading to 12a and methyl bromide (Fig. 3). This step is followed by angular methylation (9-11) of 12a. It would not be surprising for such a reaction to have a very high preference for producing cis fusion. Clearly, a great deal of ring strain would be introduced in any transition state en route to trans-fused products.Whereas the enolate alkylation proposal is presumptive, several alternate formulations merited consideration. In principle, one can envision the possibility that lithium enolate 12a is not actually produced (perhaps due to ring strain). Rather, 11 (Fig. 3) arises from the merger of otherwise high-energy species en route to 12a and 12b. For instance, "radicaloid" (5) character could be generated at both the bridgehead ...

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“…On the basis of literature data, 14 should have 99.8 % of the conformer with both groups in the equatorial position, at equilibrium. On the basis of literature data, 14 should have 99.8 % of the conformer with both groups in the equatorial position, at equilibrium.…”

Section: Cis-i Trans1mentioning

confidence: 98%

Chloride-induced elimination from 2-phenylcyclopentyl, 2-phenylcyclohexyl, and 2-norbornyl brosylates in acetone

Beltrame¹,

Ceccon²,

Winstein³

1972

J. Am. Chem. Soc.

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Synthesen in der hydroaromatischen Reihe. VI. Die Addition von 1‐Vinyl‐6‐methoxy‐3,4‐dihydro‐naphtalin an Δ₁‐Cyclopentenon und an Δ₁‐4,4′‐Dibrom‐cyclopenten‐dion‐3,5

Abstract: I n der 2. Mitteilungl) dieser Reihe haben wir die Darstellung des Z-Vinyl-6-methozy-3,4-dihydro-nuphtalins (I)

Cited by 32 publications

References 6 publications

Axially Chiral Amidinium Ions as Inducers of Enantioselectivity in Diels−Alder Reactions

Axially Chiral Amidinium Ions as Inducers of Enantioselectivity in Diels−Alder Reactions

Stereospecific cis- and trans -ring fusions arising from common intermediates

Chloride-induced elimination from 2-phenylcyclopentyl, 2-phenylcyclohexyl, and 2-norbornyl brosylates in acetone

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Synthesen in der hydroaromatischen Reihe. VI. Die Addition von 1‐Vinyl‐6‐methoxy‐3,4‐dihydro‐naphtalin an Δ1‐Cyclopentenon und an Δ1‐4,4′‐Dibrom‐cyclopenten‐dion‐3,5

Abstract: I n der 2. Mitteilungl) dieser Reihe haben wir die Darstellung des Z-Vinyl-6-methozy-3,4-dihydro-nuphtalins (I)

Cited by 32 publications

References 6 publications

Axially Chiral Amidinium Ions as Inducers of Enantioselectivity in Diels−Alder Reactions

Axially Chiral Amidinium Ions as Inducers of Enantioselectivity in Diels−Alder Reactions

Stereospecific cis- and trans -ring fusions arising from common intermediates

Chloride-induced elimination from 2-phenylcyclopentyl, 2-phenylcyclohexyl, and 2-norbornyl brosylates in acetone

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Synthesen in der hydroaromatischen Reihe. VI. Die Addition von 1‐Vinyl‐6‐methoxy‐3,4‐dihydro‐naphtalin an Δ₁‐Cyclopentenon und an Δ₁‐4,4′‐Dibrom‐cyclopenten‐dion‐3,5