Asymmetric Allylation of Glycidols Mediated by Allyl Acetate via Iridium-Catalyzed Hydrogen Transfer

Abstract

Glycidols prepared via Sharpless asymmetric epoxidation participate in asymmetric redox-neutral carbonyl allylation with good levels of catalyst-directed diastereoselectivity. Equally stereoselective allylations may be performed from the aldehyde oxidation level using 2-propanol as the terminal reductant. An epoxide ring opening reaction using AlMe3-n-BuLi is used to prepare the propionate-based stereotetrad spanning C17–C23 of dictyostatin, illustrating how this method may be applied to polyketide construction.

A Flexible Synthesis of Polypropionates via Diastereodivergent Reductive Ring‐Opening of Trisubstituted Secondary Glycidols

“…Additions to stereochemically more complex aldehydes have remained unexplored. Krische ’s excellent Ir‐catalyzed allylation, which is known to be effective for disubstituted epoxides, failed to give the desired products from both Sharpless epoxyalcohols and epoxyaldehydes [10] …”

Catalytic Enantioselective Carbonyl Allylation and Propargylation via Alcohol-Mediated Hydrogen Transfer: Merging the Chemistry of Grignard and Sabatier

“…Using cyclometalated π-allyliridium C , O -benzoate complexes, diverse enantioselective alcohol C–H functionalizations were developed (Scheme B). − As illustrated in the catalytic mechanism (Scheme A), the internal carboxylate of the o - C , O -benzoate moiety maintains the neutrality of the π-allyliridium intermediate and hence its nucleophilic character. Dehydrogenation of the secondary alcohol products is prevented by internal chelation of the homoallylic olefin.…”

Catalytic Nucleophilic Allylation Driven by the Water–Gas Shift Reaction

“…19 Through the use of these iridium catalysts, the formation of enantioenriched products containing quaternary stereocenters, 20 the hydroxylmethylation of allylic acetates by enantio-topic π -facial discrimination, 21 and asymmetric allylation of glycidols while avoiding the common match-mismatch concerns 22 can be efficiently conducted. Also highlighted is the precise chemoselectivity that this method entails as demonstrated through the enantioselective allylation at the site of a single alcohol in a polyol without the need for protecting groups.…”

“…For example, Krische and co-workers have developed a highly efficient and selective catalytic allylation of aldehydes that employs an iridium-based, transfer hydrogenation catalyst to produce homoallylic alcohols in high yield and enantioselectivity starting from allylic acetates, dienes, or allenes . Through the use of these iridium catalysts, the formation of enantioenriched products containing quaternary stereocenters, the hydroxylmethylation of allylic acetates by enantiotopic π-facial discrimination, and asymmetric allylation of glycidols while avoiding the common match-mismatch concerns can be efficiently conducted. Also highlighted is the precise chemoselectivity that this method entails as demonstrated through the enantioselective allylation at the site of a single alcohol in a polyol without the need for protecting groups .…”