Development of an Elegant, Thermally Benign Johnson-Claisen Rearrangement

Kelly Cosgrove (2010). Development of an Elegant, Thermally Benign Johnson-Claisen Rearrangement PhD Thesis, School of Chemistry & Molecular Bioscience, The University of Queensland.

       
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Author Kelly Cosgrove
Thesis Title Development of an Elegant, Thermally Benign Johnson-Claisen Rearrangement
School, Centre or Institute School of Chemistry & Molecular Bioscience
Institution The University of Queensland
Publication date 2010-01
Thesis type PhD Thesis
Supervisor Dr Ross McGeary
Total pages 149
Total colour pages 16
Total black and white pages 133
Subjects 03 Chemical Sciences
Abstract/Summary The Johnson-Claisen rearrangement is a valuable method for the formation of new carbon-carbon bonds, however the rearrangement suffers from high reaction temperatures and prolonged reaction times. On the basis of previous research into substituent-induced rate enhancements of the Claisen rearrangement, we aimed to reduce the severity of the Johnson-Claisen conditions by applying this reaction to allylic cyanohydrins. Application of the standard Johnson-Claisen conditions (excess of orthoester and catalytic protic acid) to allylic cyanohydrins resulted in their decomposition to a,b- unsaturated aldehydes. The anticipated d-ethoxycarbonyl-a,b-unsaturated nitriles were formed in trace amounts. Subsequent optimisation of this reaction has allowed a practical entry into a,b- unsaturated nitriles in reasonable yields, however high reaction temperatures were necessary for an efficient conversion. Clearly, a change of approach was desired; we have since discovered that mixed orthoesters derived from allylic alcohols undergo methanol elimination in the presence of triisobutylaluminium (TIBAL) at room temperature to form mixed ketene acetals. TIBAL then promotes immediate Claisen rearrangement of these intermediates, and subsequent reduction of the ester products to yield, g,d- unsaturated primary alcohols in a convenient one-pot procedure, with yields ranging from 52-81% and with a range of functional group tolerance.
Keyword Cyanohydrin, Johnson-Claisen rearrangement, allylic alcohol, mixed orthoester,
Additional Notes Colour pages: 13, 26, 28, 51, 79, 110-119, 139. Landscape pages: 110-118.

 
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Created: Wed, 19 May 2010, 20:15:06 EST by Ms Kelly Cosgrove on behalf of Library - Information Access Service