Abstract
Here, we present a new stereoselective alkylation of titanium(IV) enolates of chiral N-acyl oxazolidinones with tert-butyl peresters from Cα-branched aliphatic carboxylic acids, which proceeds through the decarboxylation of the peresters and the subsequent formation of alkyl radicals to produce the alkylated adducts with an excellent diastereoselectivity. Theoretical calculations account for the observed reactivity and the outstanding stereocontrol. Importantly, the resultant compounds can be easily converted into ligands for asymmetric and catalytic transformations.
Highlights
We present a new stereoselective alkylation of titanium(IV) enolates of chiral N-acyl oxazolidinones with tert-butyl peresters from Cα-branched aliphatic carboxylic acids, which proceeds through the decarboxylation of the peresters and the subsequent formation of alkyl radicals to produce the alkylated adducts with an excellent diastereoselectivity
It is certainly true that successful methods based on the alkylation of metal enolates and enamines are widespread, but they are usually restricted to a privileged set of alkylating agents, namely sterically unhindered and active alkyl halides or sulfonates, able to react through an SN2-like mechanism.[3−5] Alternative methods based on an SN1like mechanism have been reported, but they mostly require stabilized carbenium or oxocarbenium intermediates.[6−8] As a result, the chemo- and stereoselective introduction of any secondary or tertiary alkyl groups continues to be an unresolved issue.[9]
The feasibility of such an approach was clearly demonstrated in the alkylation of chiral N-acyl oxazolidinones with diacyl peroxides (Scheme 1).[12−14] diacyl peroxides from α-branched aliphatic carboxylic acids are difficult to manipulate, which made the reaction with tertiary alkyl groups elusive
Summary
We present a new stereoselective alkylation of titanium(IV) enolates of chiral N-acyl oxazolidinones with tert-butyl peresters from Cα-branched aliphatic carboxylic acids, which proceeds through the decarboxylation of the peresters and the subsequent formation of alkyl radicals to produce the alkylated adducts with an excellent diastereoselectivity. The feasibility of such an approach was clearly demonstrated in the alkylation of chiral N-acyl oxazolidinones with diacyl peroxides (Scheme 1).[12−14] diacyl peroxides from α-branched aliphatic carboxylic acids are difficult to manipulate, which made the reaction with tertiary alkyl groups elusive.
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