| dc.description.abstract | The rate of the base-catalyzed transesterification of
sucrose and ethyl myristate was shown to vary somewhat
as a function of solvent and base catalyst, but the
most significant effect was the 2-4 fold acceleratin caused
by the presence of crown ether. Nevertheless,
the transesterification product consisted of three
monoesters of sucrose (derived from the primary alcohol
functions), and a mixture of five minor components.
The major product of these transesterification reactions
was the 6 ester obtained in ca. 66% yield. Similarly,
both methyl a- and 6-glucopyranosides gave 46 and 37%
yields of the 6-monoesters. The transesterification of ...
several 4,6-benzal derivatives of hexopyranosides gave
mixtures of the 2-0- and 3-0-esters and furthermore the
experimental conditions also,.caused isomerization by the
shift of acyl_ groups among the neighboring hydroxyl groups. --
Similar results were obtained by using acylimidazoles ,and
other such acylating agents.
2. The reported faiJure of lactose to give base catalyzed
transesterification was confirmed and prompted the
examination of the methyl 6-lactoside in this reaction.
The product consisted of two mono- and two diesters. The
monoesters are believed to be the 3
, - and 6- derivatives
of the galactose portion, while the diesters are thought
to be the 6,6' – and 3`,6 - compounds.
3. Excellent seletive esterification at the 2-0- position
was achieved by al1owing a series of mono- and
disaccharides to react with dibutyltin oxide, and by
treating the resulting dibutyistannylene with acid
halides. It appeats the preferential formation and
reactivity of the stannylene derivatives depends on the
coordination of the anomeric oxygen with tin complexed
by the 2,3-hydroxyl groups. This requirement explains
that .the selective acylation was limited to a.-substituted
saccharides with the R configuration at C-2.
4. A benzalation procedure that functions under non-acidic
conditions was developed by using the dithioacetal
derived from benzaldehyde and 1,2-ethanedithiol as well
as its disulfonium salts. This reaction was applied to
a series of diols and monosaccharides. The application of
the procedure to sucrose apparently gave a poor yield of
the 4,6-0-benzylidene deiivative isolated as the hexaacetate.
5. The NMR spectra of the benzal derivatives prepared in this
work showed a variation of the chemical shift of the
PhCH signal with ring size and the presence of substituents.
An attempt was made to rationalize the observed chemical
shift differences in terms of buttressing and other longrange
effects. | en |
