Abstract
An asymmetric synthesis of 3-aryl-3,4-dihydroisocoumarins using the reaction of laterally lithiated 4,4-dimethyl-2-(o-tolyl)oxazoline with aromatic aldehydes, in the presence of an external chiral ligand, gave products with enantiomeric excess (ee) in the range of 60-70%.
Highlights
The 3-aryl-3,4-dihydroisocoumarins 1 constitute a class of natural products, which exhibit a wide range of pharmacological activities such as antifungal, antiulcer, antileukemic, antiallergic, differentiation-inducing and antimalarial activities.[1]
In the majority of these approaches the chiral moiety is present in the substrate and needs removal after reaction.2a-g Recently, Kurosaki et al reported the stereoselective addition of laterally lithiated (S)-4-isopropyl-2-(o-tolyl)oxazoline to aldehydes followed by diastereomer-selective lactonization and obtained 1 with good to high optical activity (Scheme 1).[3]
We investigated the reaction of o-toluic acid 4 with benzaldehyde using n-BuLi as base and (-)-sparteine as external chiral ligand at -78 °C (Scheme 2; Equation 1)
Summary
The 3-aryl-3,4-dihydroisocoumarins 1 constitute a class of natural products, which exhibit a wide range of pharmacological activities such as antifungal, antiulcer, antileukemic, antiallergic, differentiation-inducing and antimalarial activities.[1]. Abstract An asymmetric synthesis of 3-aryl-3,4-dihydroisocoumarins using the reaction of laterally lithiated 4,4-dimethyl-2-(o-tolyl)oxazoline with aromatic aldehydes, in the presence of an external chiral ligand, gave products with enantiomeric excess (ee) in the range of 60-70%.
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