?url_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Adc&rft.relation=http%3A%2F%2Fd-scholarship-dev.library.pitt.edu%2F10131%2F&rft.title=PROCESSING+OF+THE+DIBAL+ADDUCT+OF+A+PROLINE-DERIVED+ESTER+TO+GENERATE+A+SINGLE+DIASTEREOMER+OF+AN+ALLYL+ALCOHOL+FOR+USE+IN+A+NOVEL+SYNTHETIC+METHOD+FOR+PYRROLIZIDINES&rft.creator=Zhao%2C+Yang&rft.description=Using+the+method+of+intramolecular+carbolithiation+in+which+the+organolithium+is+generated+by+reductive+lithiation+of+a+phenyl+thioether%2C+annulations+on+to+pyrrolidine+derivatives+have+been+accomplished+to+produce+virtually+enantiomerically+and+diastereomerically+pure+pyrrolizidines.+However%2C+the+main+part+of+the+thesis+involves+mechanistic+and+theoretical+studies+of+the+highly+diastereoselective+process+by+which+a+key+intermediate%2C+(S%2CS)-2-pyrrolidinyl+vinyl+carbinol+6%2C+in+the+synthesis+of+a+hydroxylated+pyrrolizidine%2C+is+generated+from+N-Boc-L-proline+methyl+ester.The+process+involves+the+treatment+of+this+ester+with+DIBAL+at+-78+%C2%A1%C3%A3C%2C+warming+to+-20+%C2%A1%C3%A3C%2C+cooling+to+-78+%C2%A1%C3%A3C%2C+and+treatment+with+vinylmagnesium+bromide.+It+was+demonstrated+that+there+is+virtually+no+stereoselectivity+when+the+vinylmagnesium+bromide+is+added+to+the+corresponding+aldehyde+in+the+presence+of+di-isobutylaluminum+methoxide%2C+the+products+expected+if+the+DIBAL-ester+adduct+decomposes+before+Grignard+addition.+Further+evidence+that+an+aldehyde+is+not+involved+was+obtained+when+it+could+not+be+detected+by+1H+NMR+in+the+solution+after+warm-up.+The+theoretical+study+was+designed+to+test+a+postulated+mechanism+in+which+a+mixture+of+diastereomeric+adducts+R1+and+R2+of+DIBAL+and+the+ester%2C+generated+at+-78+%C2%A1%C3%A3C%2C+undergoes+equilibration+by+reversible+ionization+of+the+methoxide+ion+when+warmed+and+that+the+isomer+R1+greatly+predominates+at+equilibrium.+Both+diastereomers+are+believed+to+involve+a+seven-membered+ring%2C+afforded+by+coordination+of+the+Al+atom+of+the+adduct+with+the+carbonyl+oxygen+atom+of+the+Boc+group%2C+fused+to+the+pyrrolidine.+Reaction+of+the+diastereomer+R1+with+vinylmagnesium+bromide+via+a+SNi+mechanism+would+yield+the+observed+diastereomer+of+the+allylic+alcohol.Calculations+do+indeed+predict+that+R1+is+substantially+more+stable+than+its+diastereomer+R2+providing+evidence+for+the+mechanism.+As+a+bonus%2C+it+has+been+discovered+that+the+same+high+stereoselectivity+can+be+attained+without+raising+the+temperature+by+adding+a+catalytic+amount+of+the+Lewis+acid+ZnCl2+at+-78+%C2%A1%C3%A3C%3B+the+Lewis+acid+probably+aids+the+ionization+of+the+methoxide+ion+thus+increasing+the+rate+of+equilibration%2C+providing+an+additional+piece+of+evidence+for+the+mechanism+as+well+as+simplifying+the+experimental+procedure.&rft.date=2006-06-29&rft.type=University+of+Pittsburgh+ETD&rft.type=PeerReviewed&rft.format=application%2Fpdf&rft.language=en&rft.identifier=http%3A%2F%2Fd-scholarship-dev.library.pitt.edu%2F10131%2F1%2FZhaoYang.pdf&rft.identifier=++Zhao%2C+Yang++(2006)+PROCESSING+OF+THE+DIBAL+ADDUCT+OF+A+PROLINE-DERIVED+ESTER+TO+GENERATE+A+SINGLE+DIASTEREOMER+OF+AN+ALLYL+ALCOHOL+FOR+USE+IN+A+NOVEL+SYNTHETIC+METHOD+FOR+PYRROLIZIDINES.++Master's+Thesis%2C+University+of+Pittsburgh.++++(Unpublished)++