Related Experiment Video
Updated: Aug 1, 2026
14:55
Atomic Scale Structural Studies of Macromolecular Assemblies by Solid-state Nuclear Magnetic Resonance Spectroscopy
Published on: September 17, 2017
Terpestacin core structure. control of stereochemistry
Gideon O Berger1, Marcus A Tius
1Department of Chemistry, 2545 The Mall, University of Hawaii, Honolulu, 96822, USA.
Organic Letters
|October 21, 2005
Summary
Researchers synthesized the alpha-hydroxycyclopentenone core of terpestacin using an allene ether Nazarov cyclization. This method controls stereochemistry, extending the scope of cationic cyclopentannelation reactions.
Area of Science:
- Organic Chemistry
- Synthetic Chemistry
Background:
- Terpestacin is a natural product with a complex alpha-hydroxycyclopentenone core.
- Efficient synthetic routes are needed to access terpestacin and its analogs.
Purpose of the Study:
- To develop a novel synthetic strategy for the alpha-hydroxycyclopentenone core of terpestacin.
- To explore the utility of allene ether Nazarov cyclization in constructing this core structure.
- To investigate the control of stereochemistry during the synthesis.
Main Methods:
- Allene ether Nazarov cyclization of an alkylidene-gamma-butyrolactone.
- Regio- and stereoselective alkylation reactions.
- Utilizing E-alkylidene-gamma-butyrolactones as substrates.
Main Results:
- Successful preparation of the alpha-hydroxycyclopentenone core structure in a model system.
- Demonstrated control of stereochemistry at key positions (C1, C15, C23) based on terpestacin numbering.
- The use of E-isomers expanded the applicability of the cationic cyclopentannelation reaction.
Conclusions:
- The developed allene ether Nazarov cyclization provides an effective route to the terpestacin core.
- This methodology offers a powerful tool for stereocontrolled synthesis in organic chemistry.
- The findings contribute to the broader field of natural product synthesis and methodology development.
Related Concept Videos
02:52Stereoisomerism
Isomerism in Complexes
Isomers are different chemical species that have the same chemical formula.
Transition metal complexes often exist as geometric isomers, in which the same atoms are connected through the same types of bonds but with differences in their orientation in space. Coordination complexes with two different ligands in the cis and trans positions from a ligand of interest form isomers. For example, the octahedral [Co(NH3)4Cl2]+ ion has two isomers (Figure 1) In the cis...
Isomers are different chemical species that have the same chemical formula.
Transition metal complexes often exist as geometric isomers, in which the same atoms are connected through the same types of bonds but with differences in their orientation in space. Coordination complexes with two different ligands in the cis and trans positions from a ligand of interest form isomers. For example, the octahedral [Co(NH3)4Cl2]+ ion has two isomers (Figure 1) In the cis...
02:23SN2 Reaction: Stereochemistry
In an SN2 reaction, the nucleophilic attack on the substrate and departure of the leaving group occurs simultaneously through a transition state. As the nucleophile approaches the substrate from the back-side, the configuration of the substrate carbon changes from tetrahedral to trigonal bipyramidal and then back to tetrahedral, leading to an inversion in the configuration of the product.
If the substrate is an achiral molecule at the α-carbon, the inversion of configuration is not observed.
If the substrate is an achiral molecule at the α-carbon, the inversion of configuration is not observed.
02:15SN1 Reaction: Stereochemistry
This lesson provides an in-depth discussion of the stereochemical outcomes in an SN1 reaction.
In the first step of an SN1 reaction, the bond between the electrophilic carbon and the leaving group ionizes to generate the carbocation intermediate. The second step of the mechanism is the nucleophilic attack.
In the formed carbocation, the positively charged carbon is sp2 hybridized with a trigonal planar geometry. As all the three substituents lie on the same plane, a plane of symmetry for the...
In the first step of an SN1 reaction, the bond between the electrophilic carbon and the leaving group ionizes to generate the carbocation intermediate. The second step of the mechanism is the nucleophilic attack.
In the formed carbocation, the positively charged carbon is sp2 hybridized with a trigonal planar geometry. As all the three substituents lie on the same plane, a plane of symmetry for the...
01:17Thermal Electrocyclic Reactions: Stereochemistry
The stereochemistry of electrocyclic reactions is strongly influenced by the orbital symmetry of the polyene HOMO. Under thermal conditions, the reaction proceeds via the ground-state HOMO.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
01:26Photochemical Electrocyclic Reactions: Stereochemistry
The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
Selection Rules: Photochemical Activation
Selection Rules: Photochemical Activation
01:33Radical Halogenation: Stereochemistry
Stereochemistry is the study of the different spatial arrangements of atoms in a given molecule. The stereochemistry of radical halogenations can be understood from three different situations:
Halogenation to form a new chiral center:
Halogenation to form a new chiral center: