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(DTBMP) to form fused bis(pyran) product
26
(Scheme 15.9). On the other hand,
when TMSOTf is used the
exo
-mode of oxacyclization takes place to furnish
product
27
[82].
Scheme 15.9
Divergent oxacyclization of tris-epoxide
25.
In 2000, Corey and coworkers reported an enantioselective total synthesis of
glabrescol (
32
) and its structure elucidation (Scheme 15.10) [83, 84]. Tetraene
29
was epoxidized with ketone
1
to give tetraepoxide
30,
which underwent acid-
catalyzed cyclization to form tetraol
31.
Glabrescol (
32
) was obtained in two steps
from tetraol
31.
In 2007, Jamison and coworkers reported on epoxide-opening
cascades promoted by water at 70 °C [85]. Under the reaction conditions, formation
of desired tetrahydropyran is favored over the formation of tetrahydrofuran. The
Scheme 15.10
Synthesis of glabrescol (
32
).
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