The Conjugate Addition- Elimination Reaction of Morita-Baylis-Hillman C- Adducts: A Density Functional Theory Study

Handle URI:
http://hdl.handle.net/10754/273096
Title:
The Conjugate Addition- Elimination Reaction of Morita-Baylis-Hillman C- Adducts: A Density Functional Theory Study
Authors:
Tan, Davin
Abstract:
The Morita-Baylis-Hillman (MBH) reaction is a very versatile synthetic protocol to synthesize various useful compounds containing several functional groups. MBH acetates and carbonates are highly valued compounds as they have good potential to be precursors for organic synthesis reactions due to their ease of modification and synthesis. This thesis utilizes Density Functional Theory (DFT) calculations to understand the mechanism and selectivity of an unexpected tandem conjugate addition-elimination (CA-E) reaction of allylic alkylated Morita-Baylis-Hillman C- adducts. This synthetic protocol was developed by Prof. Zhi-Yong Jiang and co-workers from Henan University, China. The reaction required the use of sub-stoichiometric amounts of an organic or inorganic Brøndst base as a catalyst and was achieved with excellent yields (96%) in neat conditions. TBD gave the highest yield amongst the organocatalysts and Cs2CO3 gave the highest yield amongst all screened bases. A possible mechanistic pathway was proposed and three different energy profiles were modeled using 1,5,7-triaza-bicyclo-[4.4.0]-dec-5-ene (TBD), Cs2CO3 and CO32- as catalysts. All three models were able to explain the experimental observations, revealing both kinetic and thermodynamic factors influencing the selectivity of the CA-E reaction. CO32- model gave the most promising result, revealing a significant energy difference of 17.9 kcal/mol between the transition states of the two differing pathways and an energy difference of 20.9 kcal/mol between the two possible products. Although TBD modeling did not show significant difference in the transition states of the differing pathways, it revealed an unexpected secondary non-covalent electrostatic interaction, involving the electron deficient C atom of the triaza CN3 moiety of the TBD catalyst and the O atom of a neighboring NO2- group in the intermediate. Subsequent modeling using a similar substrate proved the possibility of this non-covalent electrostatic interaction, as there was significant overlap of the orbital cloud present in both the Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO) of the molecule between the C atom of the triaza moiety belonging to the TBD catalyst and the O atom of the nitro group of the substrate. The Mayer bond order was of the C-O interaction was determined to be 0.138.
Advisors:
Huang, Kuo-Wei ( 0000-0003-1900-2658 )
Committee Member:
Eppinger, Jörg ( 0000-0001-7886-7059 ) ; Lai, Zhiping ( 0000-0001-9555-6009 )
KAUST Department:
Physical Sciences and Engineering (PSE) Division
Program:
Chemical Sciences
Issue Date:
Dec-2011
Type:
Thesis
Appears in Collections:
Theses; Physical Sciences and Engineering (PSE) Division; Chemical Science Program

Full metadata record

DC FieldValue Language
dc.contributor.advisorHuang, Kuo-Weien
dc.contributor.authorTan, Davinen
dc.date.accessioned2013-03-16T08:21:52Zen
dc.date.available2013-03-16T08:21:52Zen
dc.date.issued2011-12en
dc.identifier.urihttp://hdl.handle.net/10754/273096en
dc.description.abstractThe Morita-Baylis-Hillman (MBH) reaction is a very versatile synthetic protocol to synthesize various useful compounds containing several functional groups. MBH acetates and carbonates are highly valued compounds as they have good potential to be precursors for organic synthesis reactions due to their ease of modification and synthesis. This thesis utilizes Density Functional Theory (DFT) calculations to understand the mechanism and selectivity of an unexpected tandem conjugate addition-elimination (CA-E) reaction of allylic alkylated Morita-Baylis-Hillman C- adducts. This synthetic protocol was developed by Prof. Zhi-Yong Jiang and co-workers from Henan University, China. The reaction required the use of sub-stoichiometric amounts of an organic or inorganic Brøndst base as a catalyst and was achieved with excellent yields (96%) in neat conditions. TBD gave the highest yield amongst the organocatalysts and Cs2CO3 gave the highest yield amongst all screened bases. A possible mechanistic pathway was proposed and three different energy profiles were modeled using 1,5,7-triaza-bicyclo-[4.4.0]-dec-5-ene (TBD), Cs2CO3 and CO32- as catalysts. All three models were able to explain the experimental observations, revealing both kinetic and thermodynamic factors influencing the selectivity of the CA-E reaction. CO32- model gave the most promising result, revealing a significant energy difference of 17.9 kcal/mol between the transition states of the two differing pathways and an energy difference of 20.9 kcal/mol between the two possible products. Although TBD modeling did not show significant difference in the transition states of the differing pathways, it revealed an unexpected secondary non-covalent electrostatic interaction, involving the electron deficient C atom of the triaza CN3 moiety of the TBD catalyst and the O atom of a neighboring NO2- group in the intermediate. Subsequent modeling using a similar substrate proved the possibility of this non-covalent electrostatic interaction, as there was significant overlap of the orbital cloud present in both the Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO) of the molecule between the C atom of the triaza moiety belonging to the TBD catalyst and the O atom of the nitro group of the substrate. The Mayer bond order was of the C-O interaction was determined to be 0.138.en
dc.language.isoenen
dc.subjectDensity Functional Theoryen
dc.subjectTBDen
dc.subjectMorita-Baylis-Hillmanen
dc.subjectConjugate addition eliminationen
dc.subjectGuanidineen
dc.subjectConjugate= addition eliminationen
dc.subjectConformational analysisen
dc.titleThe Conjugate Addition- Elimination Reaction of Morita-Baylis-Hillman C- Adducts: A Density Functional Theory Studyen
dc.typeThesisen
dc.contributor.departmentPhysical Sciences and Engineering (PSE) Divisionen
thesis.degree.grantorKing Abdullah University of Science and Technologyen_GB
dc.contributor.committeememberEppinger, Jörgen
dc.contributor.committeememberLai, Zhipingen
thesis.degree.disciplineChemical Sciencesen
thesis.degree.nameMaster of Scienceen
dc.person.id113623en
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