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Updated: May 21, 2026
09:35
Preparation of a Corannulene-functionalized Hexahelicene by Copper(I)-catalyzed Alkyne-azide Cycloaddition of Nonplanar Polyaromatic Units
Published on: September 18, 2016
Regiodivergent 1,3-Annulation of Valylene with 4-Hydroxycoumarins.
Yong-Kang Mei1,2, Zhi-Yuan Ding1,2, Yilitabaier Julaiti1,2
1Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian 116023, China.
Organic Letters
|May 20, 2026
Summary
Researchers developed an efficient synthesis for novel pyranocoumarins using catalytic annulation. This method offers a versatile platform for creating diverse pyranocoumarin structures with high selectivity.
Area of Science:
- Organic Chemistry
- Synthetic Chemistry
- Natural Product Synthesis
Background:
- Pyranocoumarins are natural products with significant biological activities.
- Efficient synthesis of pyranocoumarins is crucial for exploring their potential applications.
- Existing synthetic methods may lack selectivity or efficiency.
Purpose of the Study:
- To develop an efficient catalytic method for synthesizing new dimethylallyl-decorated pyranocoumarins.
- To investigate the regioselectivity of the annulation reaction under different catalytic conditions.
- To establish a robust platform for generating diverse pyranocoumarin scaffolds.
Main Methods:
- Catalytic formal [3 + 3] annulation of 4-hydroxycoumarins with valylene.
- Utilized acid catalysis for 1,3-alkenoxylation and Rh catalysis for 3,1-alkenoxylation.
- Performed mechanistic studies to elucidate the reaction pathway.
Main Results:
- Successfully synthesized two new types of dimethylallyl-decorated pyranocoumarins.
- Achieved exclusive 1,3-alkenoxylation under acid catalysis, yielding angular pyranocoumarins.
- Demonstrated Rh catalysis-induced switch in regioselectivity to 3,1-alkenoxylation.
- The protocol exhibited high atom-economy, readily available substrates, and excellent regio- and chemo-selectivity.
Conclusions:
- The developed protocol provides an efficient and selective method for pyranocoumarin synthesis.
- The reaction proceeds through regioselective hydroalkoxylation and intramolecular cyclization.
- This work offers a valuable strategy for addressing selectivity challenges and constructing diverse pyranocoumarin structures.
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01:16[4+2] Cycloaddition of Conjugated Dienes: Diels–Alder Reaction
The Diels–Alder reaction is an example of a thermal pericyclic reaction between a conjugated diene and an alkene or alkyne, commonly referred to as a dienophile. The reaction involves a concerted movement of six π electrons, four from the diene and two from the dienophile, forming an unsaturated six-membered ring. As a result, these reactions are classified as [4+2] cycloadditions.
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01:21[3,3] Sigmatropic Rearrangement of 1,5-Dienes: Cope Rearrangement
The Cope rearrangement is classified as a [3,3] sigmatropic shift in 1,5-dienes, leading to a more stable, isomeric 1,5-diene. The reaction involves a concerted movement of six electrons, four from two π bonds and two from a σ bond, via an energetically favorable chair-like transition state.
01:16Structure of Conjugated Dienes
Introduction
Conjugated dienes are compounds characterized by the presence of alternating double and single bonds. In a conjugated system like 1,3-butadiene, the unhybridized 2p orbital on each carbon overlaps continuously, allowing the π electrons to be delocalized across the entire molecule. In contrast, this type of overlap does not occur in cumulated and isolated dienes, such as 2,3-pentadiene and 1,4-pentadiene, respectively. Instead, the π electrons remain localized between the double...
Conjugated dienes are compounds characterized by the presence of alternating double and single bonds. In a conjugated system like 1,3-butadiene, the unhybridized 2p orbital on each carbon overlaps continuously, allowing the π electrons to be delocalized across the entire molecule. In contrast, this type of overlap does not occur in cumulated and isolated dienes, such as 2,3-pentadiene and 1,4-pentadiene, respectively. Instead, the π electrons remain localized between the double...
02:36Regioselectivity and Stereochemistry of Hydroboration
A significant aspect of hydroboration–oxidation is the regio- and stereochemical outcome of the reaction.
Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn stereochemistry.
Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn stereochemistry.
01:57Preparation of Diols and Pinacol Rearrangement
Compounds bearing two hydroxyl groups are known as diols. When the hydroxyl groups are located on adjacent carbon atoms, the diols are called vicinal diols or glycols. Under acidic conditions, vicinal diols undergo a specific reaction called pinacol rearrangement.
The reaction begins with transferring a proton from the acid catalyst to one of the hydroxyl groups, producing an oxonium ion.
The reaction begins with transferring a proton from the acid catalyst to one of the hydroxyl groups, producing an oxonium ion.
01:28Stability of Conjugated Dienes
Introduction
A comparison of the enthalpies of hydrogenation of dienes reveals that conjugated dienes release less heat on hydrogenation, rendering them more stable than their nonconjugated analogs.
A comparison of the enthalpies of hydrogenation of dienes reveals that conjugated dienes release less heat on hydrogenation, rendering them more stable than their nonconjugated analogs.