COMPUTATIONAL STUDIES OF DISUBSTITUTED BICYCLO[m.m.m]ALKANE AND DISUBSTITUTED BICYCLO[8.8.n]ALKANES, SYNTHESIS OF 1,10-DIMETHYLBICYCLO[8.8.8]HEXACOSANE AND 1,10-DIHYDROXYBICYCLO[8.8.8]HEXACOSANE, AND PROGRESS TOWARDS THE SYNTHESIS OF A DISUBSTITUTED 1,10-
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azu_etd_10153_sip1_m.pdf
Issue Date
2008Keywords
Bicyclo[8.8.8]hexacosaneBicyclo[8.8.n]alkane
Bicyclo[m.m.m]alkane
Conformational Analysis
Elastomer
Novel Polymer
Committee Chair
Mash Jr., Eugene A.Metadata
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The University of Arizona.Rights
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.Abstract
Polymers possess bulk elastic properties due to entanglement of the polymer chains, not due to an inherit elasticity found within the monomers. An appropriately disubstituted bicyclo[8.8.8]hexacosane monomer should impart inherit elasticity when utilized in a polymer. A stochastic search of disubstituted bicyclo[m.m.m]alkanes demonstrated that these systems will adopt an out,out configuration and bicycles with medium and large values of m possess variable bridgehead-bridgehead distances. A stochastic search of disubstituted bicyclo[8.8.n]alkanes demonstrated an even-odd effect within the bite-angle of the bicycle. Two model compounds with methyl and hydroxyl groups at the bridgehead carbons were synthesized that demonstrated solid-state structures that correlated extremely well with the computational search. The solid-state structures were observed with both an out,out configuration and variable bridgehead-bridgehead distances. To investigate this hypothesis, polyurethanes will be made from the following diol monomers: 1,10-decanediol, a monocyclic diol, and a bicyclo[8.8.8]hexacosane diol.Type
textElectronic Dissertation
Degree Name
Ph.D.Degree Level
doctoralDegree Program
ChemistryGraduate College
Degree Grantor
University of ArizonaCollections
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Diastereoselective manipulations and conformational calculations of enantiomerically pure bicyclo(M.1.0)alkan-2-ones and bicyclo(M.1.0)alk-3-en-2-ones.Medium- and large-sized cycloalkanones with adjacent fused cyclopropyl rings are excellent substrates for highly diastereoselective reactions. We attribute the high selectivity of these reactions to local conformational rigidity around the stereo genic cyclopropane ring in these otherwise flexible systems. Addition of a variety of nucleophiles to these compounds, where the large ring ranged from eight- to 16-membered, gave cyclopropyl carbinols with >20:1 stereoselectivity. Crystallographic analysis of the products in several cases confirmed that the favored approach of the nucleophile is anti to the geometry of the ring fusion. This ability of the cyclopropyl ring to direct stereoselective reactions at carbonyl was extended to carbon atoms further around the parent ring. In initial studies, alkylations of bicyclo[6.1.0]nonan-2-one lithium enolate gave single a-alkyl ketone diastereomers. These and other bicyclic ketones have been converted to the respective α,β-unsaturated ketones and extremely high diastereoselectivity in 1,2-additions to these compounds was observed, giving the respective allylic cyclopropyl carbinols. Additionally, Michael and cuprate additions to these enones gave 1,4-adducts in good yield, with diastereoselectivity dependent on the specific reaction and the ring size. Molecular mechanics calculations were performed to model the ground state conformations of the starting ketones and enones in these reactions. In the large ensemble of conformers found in each ring size, conformers lowest in energy all tended to expose one face of the carbonyl to the surroundings. For enones, anchoring of the olefin resulted in conformers exhibiting both s-cis and s-trans configurations. For reactions where assumption of early transition states is appropriate, ground state conformers can be used as general, predictive models for diastereoselection. The generalization of these computational results makes our approach to medium and large ring functionalization a powerful tool for the synthesis of medium and large carbocyclic natural products.
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Conformational analysis and nucleophilic addition transition state modeling of bicyclo(m.1.0)alkan-2-ones and bicyclo(m.1.0)alk-3-en-2-ones.Medium and large ring bicyclo (m.1.0) alkan-2-ones and bicyclo (m.1.0) alk-3-en-2-ones are ideal starting materials for stereoselective organic synthesis. Readily available in many ring sizes and in enantiomerically pure form, such carbocyclic skeleta provide entry into numerous natural products. Reactions such as 1,2-addition, α-alkylation, and 1,4-addition have been shown to proceed with high diastereoselectivity due to local conformational anchoring of the cyclopropyl ketone function. In an effort to elucidate the mechanisms of diastereoselectivity and to augment the synthetic utility, computer modeling studies have been performed. The present work began with development of molecular mechanics parameters for the cyclopropyl ketone torsion potential. Cyclopropanes are uniquely composed of sigma bonds containing high p orbital character that are capable of conjugation with α,β pi bonds. Appropriate treatment of cyclopropyl ketone conjugation was derived from ab initio torsion driving studies. The updated force field was then coupled with Monte Carlo conformation searches to explore the three dimensional shapes available to medium and large ring cyclopropyl ketones. Rationale for the observed diastereoselectivity was developed from the starting material conformational preferences, but a more direct probe of the diastereoselectivity of 1,2-asymmetric induction was desired. An empirical force field based on ab initio transition state studies has been developed to describe kinetically controlled nucleophilic additions of methyllithium to cyclopropyl ketones. The developed molecular mechanics model was then applied to transition states constructed from starting material conformations and transition state geometries identified in the ab initio calculations. Computer modeling studies of starting material and transition state conformations are presented, and diastereoselectivity predictions based on the empirical model are compared to experimental results.
