Abstract
M.Sc.
The objective of the project described in this dissertation was to develop environmentally benign
organic transformations using aluminium triflate as a Lewis acid catalyst. The activity of
aluminium triflate had already been investigated in our labs in other reactions. The present
project was directed towards protection and deprotection of hydroxyl functions and glycosidation
of differently protected glycal substrates.
A range of alcohols and phenols was successfully protected to their corresponding
tetrahydropyranyl (THP) and tetrahydrofuranyl (THF) ethers using 3,4-Dihydro-2H-pyran
(DHP) and 2,3-Dihydrofuran (DHF) respectively. Catalytic amounts of Al(OTf)3 were employed
to drive the reaction through in the presence of dichloromethane (DCM) as a solvent. This
process allowed the preparation of a structural variety of these protected ethers, including those
of a protected D-ribose derivative. The THP and THF ethers so generated were hydrolysed back
to their corresponding alcohols using Al(OTf)3 in the presence of methanol. In all cases, the free
alcohols were isolated in excellent yields. Importantly, other acid-sensitive groups (e.g. the ring
acetal and acetonide on the ribose derivative) were retained on the more complex systems.
Aluminium triflate was also employed to catalyse the O-glycosidation of 3,4,6-tri-O-acetyl-Dglucal,
3,4,6-tri-O-acetyl-D-galactal and 3,4,6-tri-O-benzyl-D-glucal. Different alkyl and
aromatic nucleophiles were used as glycosyl acceptors in these reactions. This aspect of the
study allowed a focus on O-glycosidation leading to the synthesis of 2,3-unsaturated glycosides
via Ferrier rearrangement and 2-deoxy glycosides by direct addition of alcohol nucleophiles.
Interestingly, the work discovered a temperature-switched selective Ferrier rearrangement or
direct addition with alcohols in certain instances. This important innovation led to the idea that
this protocol may be employed in the synthesis of unsymmetrical glycal based bolaforms.
Progress in this direction shall also be detailed.