Stereoselective synthesis of all-C quaternary stereocentres using non-enolisable 1,3-dialdehydes

Abstract

The efficient synthesis of all-C quaternary centres as part of an acyclic contiguous stereoarray is a highly challenging synthetic operation. Investigations have been carried out into using non-enolisable 1,3-dialdehydes, under MgBr2•OEt2 chelation control, as small building blocks for the synthesis of all-C quaternary centre as part of a stereoarray. Initial investigations focussed on developing controlled monoadditions to non-enolisable dialdehydes with allylation, hydroxyallylation and aldol reactions to give products containing two or three contiguous stereocentres, including an all-C quaternary stereocentre, with good stereocontrol. Interestingly it was found that the diastereoselection of monoaddition was different when the dialdehyde contained a pendant benzyloxy group in contrast to a pendant trityl or TBDPS ether group. The diastereoselection of additions to dialdehydes has been rationalised by considering the reactive conformations involved to form the observed diastereoisomer products of these addition reactions. A double addition process to the non-enolisable 1,3-dialdehyde with a benzyloxy group has been described. It has been found that the second addition is highly diastereoselective and is effective with a range of nucleophiles to give products containing four or five contiguous stereocentres, including an all-C quaternary stereocentre, as part of a stereoarray. The high level of diastereoselectivity of this second addition has again been rationalised by considering the reactive conformation involved. Finally, attempts have been made toward the formation of enantioenriched stereoarrays containing an all-C quaternary stereocentre. Investigations focussed on using Evans’ BOX ligands and chiral reagents in reactions with non-enolisable 1,3-dialdehydes

More information

Identifiers

ORCID for Bruno Linclau: orcid.org/0000-0001-8762-0170

Catalogue record

Export record