2 research outputs found
Structure-reactivity study of O-tosyl Cinchona alkaloids in their new synthesis and in hydrolysis to 9-epibases : unexpected formation of cinchonicine enol tosylate accelerated by microwave activation
Get PDFNew methods for
O
-
tosylation of
the
natural
Cinchona
alkaloids
have been
discovered
as
a
biphasic
processes with Bu
3
N as a
catalyst.
The
optimized
excess of
tosy
l chloride
,
necessary for
transformation
of each
of the
four alkaloid
s
into
O
-
tosy
l derivative
, decreases
in the following
order
:
quinine, quinidine, cinchonidine and cinchonine
. The same
decreasing order has been
noticed
for
the
hy
drolysis
rate
of
the
appropriate
tosylates
to 9
-
epibases
.
D
iffic
ult conversion
of
O
-
tosy
lcinchonine
in the
hydrolytic medium
of
aq
ueous tarta
ric
acid
gives
9
-
epicinchonine
together with
parallel
formation
of
cinchonicine enol
tosylate. The latter product
is
obtained
as
the main
when
both cinchonine and cinchonidine
tosylates
react
in the presence of salicylic acid
under
controlled microwave heating
.
On the basis of X
-
ray
structure of the new alkene product,
the
stereoselective
syn
-
E2
quinuclidine
ring opening process
,
competing to
the
S
N
2 hydrolysis
is
postulated
for this transformation
