I. Reactions of cyclopropanones with alkyl azides. II. Double conjugate additions of bis-nucleophiles to quinone monoketals: Formal total synthesis of (+/-)-gelsemine
by Grecian, Scott A., Ph.D., UNIVERSITY OF KANSAS, 2007, 321 pages; 3258687

Abstract:

The Lewis acid-mediated reactions of substituted cyclopropanone acetals with alkyl azides were examined. When cyclopropanone acetal was treated with alkyl azides, N-substituted 2-azetidinones and ethyl carbamate products were obtained, arising from azide addition to the carbonyl, followed by ring expansion or rearrangement, respectively. When 2,2-dimethylcyclopropanone acetals were reacted with azides in the presence of BF3•OEt2, the products obtained were α-amino-α'-diazomethyl ketones, which arose from C2-C3 bond cleavage of the corresponding cyclopropanone, giving oxyallyl cations, that were captured by azides. Aryl-substituted cyclopropanone acetals, when subjected to these conditions, afforded [1,2,3]oxaborazoles exclusively, which were also the result of C2-C3 bond rupture, azide capture and then loss of nitrogen. In the reactions of n-hexyl-substituted cyclopropanone acetals with alkyl azides, a mixture of 2-azetidinones and regioisomeric [1,2,3]oxaborazoles were obtained. A computational study was performed to investigate the regioselectivity of azide addition in these processes.

A series of cyclohexa-2,5-dienone monoketals bearing electron-withdrawing groups was treated with diethyl malonate and other bifunctional nucleophiles in the presence of catalytic KO-t-Bu in THF. Reactions of ethyl 3-nitropropionate or diethyl malonate resulted in single conjugate addition adducts. When ethyl acetoacetate was used as a nucleophile, [3.3.1]bicyclic products were obtained in good yields. The regiochemistry of conjugate addition was dependent on the cyclohexa-2,5-dienone monoketal substitution.

When cyclohexa-2,5-dienone monoketals were treated with the lithium dianion of ethyl 3-nitropropionate, followed by mild acid, [3.2.1]bicyclooctanones were generated in preparatively useful yields. One of these adducts was regioselectively acylated and subjected to an intramolecular Heck reaction, which established the spirooxindole. One of these Heck reaction products was manipulated into advanced intermediates previously used by Fukuyama and coworkers in their total syntheses of (±)- and (+)-gelsemine. Attempts to form gelsemine's pyrrolidinyl ring through intramolecular cyclization techniques are described.

 
AdviserJeffrey Aube
SchoolUNIVERSITY OF KANSAS
SourceDAI/B 68-03, p. , Jul 2007
Source TypeDissertation
SubjectsOrganic chemistry
Publication Number3258687
Adobe PDF Access the complete dissertation:
 

» Find an electronic copy at your library.
  Use the link below to access a full citation record of this graduate work:
  http://gateway.proquest.com/openurl%3furl_ver=Z39.88-2004%26res_dat=xri:pqdiss%26rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation%26rft_dat=xri:pqdiss:3258687
  If your library subscribes to the ProQuest Dissertations & Theses (PQDT) database, you may be entitled to a free electronic version of this graduate work. If not, you will have the option to purchase one, and access a 24 page preview for free (if available).

About ProQuest Dissertations & Theses
With over 2.3 million records, the ProQuest Dissertations & Theses (PQDT) database is the most comprehensive collection of dissertations and theses in the world. It is the database of record for graduate research.

The database includes citations of graduate works ranging from the first U.S. dissertation, accepted in 1861, to those accepted as recently as last semester. Of the 2.3 million graduate works included in the database, ProQuest offers more than 1.9 million in full text formats. Of those, over 860,000 are available in PDF format. More than 60,000 dissertations and theses are added to the database each year.

If you have questions, please feel free to visit the ProQuest Web site - http://www.proquest.com - or call ProQuest Hotline Customer Support at 1-800-521-3042.