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|Title: ||Mannich and O-Alkylation reactions of tetraalkoxyresorcinarenes. The use of some products in ligand assisted reactions|
|Authors: ||Buckley, Benjamin R.|
Page, Philip C. Bulman
Elsegood, Mark R.J.
Holmes, Kathryn E.
McIldowie, Matthew J.
McGrath, Matthew J.
Poulton, Andrew M.
Sampler, Edward P.
Skelton, Brian W.
White, Allan H.
|Keywords: ||axial chirality|
|Issue Date: ||2007|
|Abstract: ||The measurement of the pKa of a racemic tetramethoxyresorcinarene explains the
failure to obtain good yields in attempted Mannich reactions of
tetraalkoxyresorcinarenes under classical reaction conditions. The failure is related to
the lack of adequate concentrations of iminium ions that results from the reduced acid
strength of tetraalkoxyresorcinarenes as compared to parent
octahydroxyresorcinarenes. However, the preparation of a series of Mannich bases
derived from racemic tetraalkoxyresorcinarenes was accomplished using aprotic
reaction conditions, including microwave assisted reactions, and using pre-formed
iminium ion intermediates. In the case of reactions using chiral bis(aminol)ethers, the
reactions gave mixtures of diastereoisomers that were separated by flash
chromatography. The absolute configurations of the enantiomerically pure
tetrabenzoxazine derivatives were established as (P,R,S) or (M,S,R), in some cases by Xray
crystallographic analysis, and by a comparison of nuclear magnetic resonance
spectroscopic data. The alkylation of racemic tetramethoxyresorcinarenes was
achieved in reactions using an excess of N-(R)-(+)-α-methylbenzyl-2-bromoacetamide in
acetonitrile containing potassium carbonate. Enantioselective ligand-assisted reactions of
aromatic aldehydes are reported using dialkylzinc reagents both in the absence and
presence of terminal alkynes.|
|Description: ||This is a pre-print. The definitive version: BUCKLEY, B. R. (2006). Mannich and O-Alkylation reactions of tetraalkoxyresorcinarenes. The use of some products in ligand-assisted reactions. European journal of organic chemistry, 22, pp. 5117-5134, is available at: http://www3.interscience.wiley.com/cgi-bin/jissue/113441701|
|Appears in Collections:||Pre-Prints (Chemistry)|
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