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<record><TEI><teiHeader><fileDesc><titleStmt><title xml:lang="en">Transition States and Origins of 1,4-Asymmetric Induction in Alkylations of 2,2,6-Trialkylpiperidine Enamines</title><author><name sortKey="Um, Joann M" sort="Um, Joann M" uniqKey="Um J" first="Joann M." last="Um">Joann M. Um</name><affiliation><nlm:aff id="A1">Department of Chemistry and Biochemistry, UCLA Los Angeles, CA 90095-1569 (USA)</nlm:aff></affiliation></author><author><name sortKey="Kaka, Naeem S" sort="Kaka, Naeem S" uniqKey="Kaka N" first="Naeem S." last="Kaka">Naeem S. Kaka</name><affiliation><nlm:aff id="A2">Department of Chemistry, Chemistry Research Laboratory University of Oxford, Mansfield Road, Oxford, OX1 3TA (UK)</nlm:aff></affiliation></author><author><name sortKey="Hodgson, David M" sort="Hodgson, David M" uniqKey="Hodgson D" first="David M." last="Hodgson">David M. Hodgson</name><affiliation><nlm:aff id="A2">Department of Chemistry, Chemistry Research Laboratory University of Oxford, Mansfield Road, Oxford, OX1 3TA (UK)</nlm:aff></affiliation></author><author><name sortKey="Houk, K N" sort="Houk, K N" uniqKey="Houk K" first="K. N." last="Houk">K. N. Houk</name><affiliation><nlm:aff id="A1">Department of Chemistry and Biochemistry, UCLA Los Angeles, CA 90095-1569 (USA)</nlm:aff></affiliation></author></titleStmt><publicationStmt><idno type="wicri:source">PMC</idno><idno type="pmid">20411546</idno><idno type="pmc">3049728</idno><idno type="url">http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3049728</idno><idno type="RBID">PMC:3049728</idno><idno type="doi">10.1002/chem.201000046</idno><date when="2010">2010</date><idno type="wicri:Area/Pmc/Corpus">000113</idno><idno type="wicri:explorRef" wicri:stream="Pmc" wicri:step="Corpus" wicri:corpus="PMC">000113</idno></publicationStmt><sourceDesc><biblStruct><analytic><title xml:lang="en" level="a" type="main">Transition States and Origins of 1,4-Asymmetric Induction in Alkylations of 2,2,6-Trialkylpiperidine Enamines</title><author><name sortKey="Um, Joann M" sort="Um, Joann M" uniqKey="Um J" first="Joann M." last="Um">Joann M. Um</name><affiliation><nlm:aff id="A1">Department of Chemistry and Biochemistry, UCLA Los Angeles, CA 90095-1569 (USA)</nlm:aff></affiliation></author><author><name sortKey="Kaka, Naeem S" sort="Kaka, Naeem S" uniqKey="Kaka N" first="Naeem S." last="Kaka">Naeem S. Kaka</name><affiliation><nlm:aff id="A2">Department of Chemistry, Chemistry Research Laboratory University of Oxford, Mansfield Road, Oxford, OX1 3TA (UK)</nlm:aff></affiliation></author><author><name sortKey="Hodgson, David M" sort="Hodgson, David M" uniqKey="Hodgson D" first="David M." last="Hodgson">David M. Hodgson</name><affiliation><nlm:aff id="A2">Department of Chemistry, Chemistry Research Laboratory University of Oxford, Mansfield Road, Oxford, OX1 3TA (UK)</nlm:aff></affiliation></author><author><name sortKey="Houk, K N" sort="Houk, K N" uniqKey="Houk K" first="K. N." last="Houk">K. N. Houk</name><affiliation><nlm:aff id="A1">Department of Chemistry and Biochemistry, UCLA Los Angeles, CA 90095-1569 (USA)</nlm:aff></affiliation></author></analytic><series><title level="j">Chemistry (Weinheim an der Bergstrasse, Germany)</title><idno type="ISSN">0947-6539</idno><idno type="eISSN">1521-3765</idno><imprint><date when="2010">2010</date></imprint></series></biblStruct></sourceDesc></fileDesc><profileDesc><textClass></textClass></profileDesc></teiHeader><front><div type="abstract" xml:lang="en"><p id="P1">The asymmetric C-alkylation of chiral enamines derived from terminal epoxides and lithium 2,2,6-trialkylpiperidides has previously been shown to provide α-alkylated aldehydes by intermolecular nucleophilic substitution in good levels of asymmetric induction. We now report a computational study of the origins of asymmetric induction in these reactions. Computational modeling with density functional theory (B3LYP/6–31G(d)) agrees closely with the experimental observations. This stereoselectivity is attributed to a preferential conformation of the enamine and the piperidine ring that places the C-6 alkyl substituent in an axial position due to A<sup>1,3</sup> strain. Preferential attack occurs away from the axial group, for steric reasons. The effects of changing the C-6 substituent from methyl to isopropyl were studied, and twist transition states were found to contribute significantly in the latter alkylations.</p></div></front></TEI><pmc article-type="research-article" xml:lang="EN"><pmc-comment>The publisher of this article does not allow downloading of the full text in XML form.</pmc-comment>
<pmc-dir>properties manuscript</pmc-dir>
<front><journal-meta><journal-id journal-id-type="nlm-journal-id">9513783</journal-id><journal-id journal-id-type="pubmed-jr-id">21686</journal-id><journal-id journal-id-type="nlm-ta">Chemistry</journal-id><journal-title>Chemistry (Weinheim an der Bergstrasse, Germany)</journal-title><issn pub-type="ppub">0947-6539</issn><issn pub-type="epub">1521-3765</issn></journal-meta><article-meta><article-id pub-id-type="pmid">20411546</article-id><article-id pub-id-type="pmc">3049728</article-id><article-id pub-id-type="doi">10.1002/chem.201000046</article-id><article-id pub-id-type="manuscript">NIHMS259293</article-id><article-categories><subj-group subj-group-type="heading"><subject>Article</subject></subj-group></article-categories><title-group><article-title>Transition States and Origins of 1,4-Asymmetric Induction in Alkylations of 2,2,6-Trialkylpiperidine Enamines</article-title></title-group><contrib-group><contrib contrib-type="author"><name><surname>Um</surname><given-names>Joann M.</given-names></name><xref ref-type="aff" rid="A1">[a]</xref></contrib><contrib contrib-type="author"><name><surname>Kaka</surname><given-names>Naeem S.</given-names><prefix>Dr.</prefix></name><xref ref-type="aff" rid="A2">[b]</xref></contrib><contrib contrib-type="author"><name><surname>Hodgson</surname><given-names>David M.</given-names><prefix>Prof.</prefix></name><xref ref-type="corresp" rid="CR2">*</xref><xref ref-type="aff" rid="A2">[b]</xref></contrib><contrib contrib-type="author"><name><surname>Houk</surname><given-names>K. N.</given-names><prefix>Prof.</prefix></name><xref ref-type="corresp" rid="CR1">*</xref><xref ref-type="aff" rid="A1">[a]</xref></contrib></contrib-group><aff id="A1"><label>[a]</label>Department of Chemistry and Biochemistry, UCLA Los Angeles, CA 90095-1569 (USA)</aff><aff id="A2"><label>[b]</label>Department of Chemistry, Chemistry Research Laboratory University of Oxford, Mansfield Road, Oxford, OX1 3TA (UK)</aff><author-notes><corresp id="CR1"><label>*</label>Fax: (+ 1) 310-206-1843 <email>houk@chem.ucla.edu</email></corresp><corresp id="CR2"><label>*</label>Fax: (+ 44) 1865-285002 <email>david.hodgson@chem.ox.ac.uk</email></corresp></author-notes><pub-date pub-type="nihms-submitted"><day>16</day><month>2</month><year>2011</year></pub-date><pub-date pub-type="ppub"><day>1</day><month>6</month><year>2010</year></pub-date><pub-date pub-type="pmc-release"><day>7</day><month>3</month><year>2011</year></pub-date><volume>16</volume><issue>21</issue><fpage>6310</fpage><lpage>6316</lpage><permissions><copyright-statement>© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim</copyright-statement><copyright-year>2010</copyright-year></permissions><abstract><p id="P1">The asymmetric C-alkylation of chiral enamines derived from terminal epoxides and lithium 2,2,6-trialkylpiperidides has previously been shown to provide α-alkylated aldehydes by intermolecular nucleophilic substitution in good levels of asymmetric induction. We now report a computational study of the origins of asymmetric induction in these reactions. Computational modeling with density functional theory (B3LYP/6–31G(d)) agrees closely with the experimental observations. This stereoselectivity is attributed to a preferential conformation of the enamine and the piperidine ring that places the C-6 alkyl substituent in an axial position due to A<sup>1,3</sup> strain. Preferential attack occurs away from the axial group, for steric reasons. The effects of changing the C-6 substituent from methyl to isopropyl were studied, and twist transition states were found to contribute significantly in the latter alkylations.</p></abstract><kwd-group><kwd>aldehydes</kwd><kwd>alkylation</kwd><kwd>asymmetric synthesis</kwd><kwd>density functional calculations</kwd><kwd>transition states</kwd></kwd-group><contract-num rid="GM1">R01 GM036700-26
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