Journal
TETRAHEDRON
Volume 61, Issue 13, Pages 3289-3303Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.tet.2005.01.103
Keywords
2-(o-tolyl)oxazoline; laterial lithiation; asymmetric synthesis; 3,4-dihydroisocoumarin; Ab initio calculation
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Lateral lithiation of (S)-4-isopropyl-2-(o-tolyl)oxazoline in diethyl ether followed by the reaction with aldehydes in the presence of TMEDA produced the addition products with stereoselectivities up to 84% de. Utilization of TMEDA as a ligand is essential for the good selectivity. Rationale for the stereoselectivity is proposed based on ab initio calculation of the lateral lithio species. The major (S,S)-products lactonized faster than the minor (S,R)-products to the corresponding 3,4-dihydroisocoumarins under acidic conditions. Thus, (3S)-3,4-dihydroisocournarins were obtained in good optical purities up to 97% ee by sequential application of these matched stereoselective reactions. (c) 2005 Elsevier Ltd. All rights reserved.
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