Eschenmoser-Claisen Rearrangement

What Is Eschenmoser-Claisen Rearrangement?

The Eschenmoser-Claisen rearrangement is a [3,3]-sigmatropic rearrangement that produces γ,δ-unsaturated amides from allylic alcohols and N,N-dimethylacetamide dimethyl acetal (DMADMA). Upon simple mixing and heating, the two components afford an amide that has been elongated by two carbon atoms via rearrangement of a ketene aminal intermediate produced in situ.

The reaction is highly stereospecific. For secondary allylic alcohols, the rearrangement proceeds with very high (E)-selectivity due to destabilizing 1,3-diaxial interactions in the transition state that would otherwise lead to the (Z)-isomer. Additionally, allylic alcohols substituted at the 2-position afford trisubstituted alkenes as products. The rearrangement typically occurs at lower temperatures (100-150 °C) than other Claisen variants, providing a more accessible thermal activation window.

• Reagents: N,N-Dimethylacetamide dimethyl acetal (orthoamide); typically heated in an inert solvent such as xylene or decalin.
• Reactants: Allylic or benzylic alcohol + N,N-dimethylacetamide dimethyl acetal.
• Products: γ,δ-Unsaturated N,N-dimethyl amide.
• Reaction Type: [3,3]-Sigmatropic rearrangement (pericyclic).
• Related Reactions: Classical Claisen rearrangement, Johnson-Claisen rearrangement (orthoesters), Ireland-Claisen rearrangement (silyl ketene acetals), Cope rearrangement.

Fig 1. Eschenmoser-Claisen rearrangement reaction and its mechanism. [1]

Mechanism of Eschenmoser-Claisen Rearrangement

1. Formation of Iminium Ion: N,N-Dimethylacetamide dimethyl acetal (the orthoamide) undergoes loss of a methoxide ion to generate an iminium cation.
2. Nucleophilic Attack by Allylic Alcohol: The allylic alcohol acts as a nucleophile and attacks the electrophilic iminium carbon, forming a new C-O bond and generating an O-alkylated intermediate.
3. Proton Transfer: A proton transfer occurs, placing the proton onto the remaining methoxide group. The methoxide then leaves as a molecule of methanol, generating another iminium cation.
4. Deprotonation and Ketene Aminal Formation: Deprotonation by methoxide (or another base present in the medium) produces a 1,5-diene species known as a ketene aminal. This highly conjugated intermediate features an N,O-ketene acetal structure that is primed for sigmatropic rearrangement.
5. [3,3]-Sigmatropic Rearrangement: The ketene aminal undergoes a pericyclic [3,3]-sigmatropic rearrangement—the hallmark step of the Claisen family—through a chair-like transition state. This concerted process results in the formation of a new carbon-carbon bond at the γ-position of the original allylic alcohol framework and delivers the final γ,δ-unsaturated amide product.

Stereochemical Considerations

One of the most valuable features of the Eschenmoser-Claisen rearrangement is its high stereoselectivity. The [3,3]-sigmatropic rearrangement proceeds through a six-membered, chair-like transition state, which dictates the stereochemical outcome of the reaction.

For secondary allylic alcohols, the (E)-isomer of the product is strongly favored over the (Z)-isomer. This selectivity arises from destabilizing 1,3-diaxial interactions in the transition state leading to the (Z)-product, whereas the transition state leading to the (E)-product is devoid of such unfavorable interactions. This stereoelectronic effect has been extensively utilized in natural product synthesis to set alkene geometry with high fidelity.

The stereospecific nature of [3,3]-sigmatropic rearrangements enables the transfer of chirality from the starting allylic alcohol to the product. When enantiomerically enriched allylic alcohols are employed, the configuration at the stereogenic center is faithfully translated into the new stereocenters formed during the rearrangement, provided that the reaction conditions do not induce racemization.

Application Examples of Eschenmoser-Claisen Rearrangement

• Example 1: Kiuchi and co-workers reported the first total synthesis of (±)-cristaxenicin A, a marine natural product with potent antiprotozoal activity against Leishmania amazonensis and Trypanosoma congolense. The nine-membered carbocyclic ring system was constructed through a one-pot sequence involving an Eschenmoser-Claisen rearrangement followed by a Cope rearrangement. Starting from 2,2-divinylcyclopentanecarbonitrile, an addition reaction with 4-(tert-butyldimethylsilyl)oxy-2-butenal set the stage for the cascade rearrangement. [2]
• Example 2: The total synthesis of brasilicardin A—a diterpene natural product with potent immunosuppressive effects—employed a diastereoselective Eschenmoser-Claisen rearrangement as a key step. The synthesis required the construction of an unusual trans-syn-trans perhydrophenanthrene skeleton, which was achieved through a sequence that included the Eschenmoser-Claisen rearrangement, a highly diastereoselective alkylation of a decalin nitrile, and a Me₂CuLi-mediated intramolecular Michael addition. [3]

Fig 2. Synthetic examples via Eschenmoser-Claisen rearrangement reaction.

Related Products

CAS No.	Structure	Product
10029-04-6		Hydroxymethylacrylicacidethylester
104-54-1		Cinnamyl Alcohol
106-24-1		Geraniol
106-25-2		Cis-3,7-Dimethyl-2,6-Octadien-1-Ol
106-28-5		(E,E)-Farnesol
111-28-4		Sorbyl alcohol
150-86-7		Phytol
1504-55-8		trans-2-Methyl-3-phenyl-2-propen-1-ol
1504-63-8		4-NITROCINNAMYL ALCOHOL
167896-48-2		trans-3-Hydroxy-1-propenylboronic acid pinacol ester
17102-64-6		trans,trans-2,4-Hexadien-1-ol
17581-85-0		3-(4-Methoxyphenyl)-2-propen-1-ol
18457-55-1		(-)-Perillyl Alcohol
18485-38-6		2,4-Dodecadien-1-ol(mixture of stereoisoers)
24034-73-9		Geranylgeraniol
24587-49-3		4-Hydroxy-but-2-enoic acid
28069-72-9		2,6-Nonadien-1-ol,(2E,6Z)-

References

1. Jie Jack Li. Name Reactions-A Collection of Detailed Mechanisms and Synthetic Applications, Sixth Edition, 2021, 100-102.
2. Kiuchi, Wataru, et al. Angewandte Chemie International Edition 65.8 (2026): e24855.
3. Wang, Zhe, et al. The Journal of Organic Chemistry 91.1 (2025): 798-802.

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