Titanium tetrachloride-mediated Diels-Alder reactions of cyclopentadiene with di-l-menthyl methylenemalonate and its acetoxy derivative as new chiral dienophiles for asymmetric induction.

Abstract

Asymmetric synthesis of [1S, 2S, 3R, 4R]-2, 3-dihydroxy-4-hydroxymethylcyclopent-1-ylmalonate (its racemic form is already known as a versatile building block for carbocyclic C-nucleosides) was achieved by Diels-Alder reaction of cyclopentadiene with di-l-menthyl acetoxymethylenemalonate, followed by retrograde aldol C-C bond fission under reductive conditions. Asymmetric induction in Diels-Alder reactions using the chiral dienophile and its nor-acetoxy derivative is discussed from a mechanistic viewpoint and a new concept for asymmetric induction is proposed.