The 1,5-HAT–1,2-(ester)alkyl
radical migration (Surzur–Tanner
rearrangement) radical/polar sequence triggered by alkoxyl radicals
has been studied on a series of
C
-glycosyl substrates
with 3-
C
-(α,β-
d
,
l
-glycopyranosyl)1-propanol
and
C
-(α-
d
,
l
-glycopyranosyl)methanol
structures prepared from chiral pool
d
- and
l
-sugar.
The use of acetoxy and diphenoxyphosphatoxy as leaving groups provides
an efficient construction of 10-deoxy-1,6-dioxaspiro[4.5]decane and
4-deoxy-6,8-dioxabicyclo[3.2.1]octane frameworks. The alkoxyl radicals
were generated by the reaction of the corresponding
N
-alkoxyphthalimides with group 14 hydrides [
n
-Bu
3
SnH(D) and (TMS)
3
SiH], and in comparative terms,
the reaction was also initiated by visible light photocatalysis using
the Hantzsch ester/
fac
-Ir(ppy)
3
procedure.
Special attention was devoted to the influence of the relative stereochemistry
of the centers involved in the radical sequence on the reaction outcome.
The addition of BF
3
•Et
2
O as a catalyst
to the radical sequence resulted in a significant increase in the
yields of the desired bicyclic ketals.