Asymmetric synthesis of 3-substituted 3,4-dihydroisocoumarins via stereoselective addition of laterally lithiated chiral 2-(o-tolyl)oxazolines to aldehydes followed by diastereomer-selective lactonization
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-dihydroisocoumarins were obtained in good optical purities up to 97% ee by sequential application of these matched stereoselective reactions.
Kurosaki, Yuji,Fukuda, Tsutomu,Iwao, Masatomo
p. 3289 - 3303
(2007/10/03)
The asymmetric synthesis of (R)-(+)- and (S)-(-)-O-methylbharatamine
The asymmetric syntheses of (R)-(+)- and (S)-(-)-O-methylbharatamine were performed using the lateral metallation strategy, in which (R)- and (S)-phenylalaninol were applied as chiral auxiliaries. The addition reaction of chiral o-toluamide carbanion to 6
Chrzanowska, Maria,Dreas, Agnieszka
p. 2561 - 2567
(2007/10/03)
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