Chemistry Reference
In-Depth Information
Table 13.5
Addition of acetylenes to cyclohexylcarbaldehyde catalyzed by Zn(OTf)
2
/
15l.
a)
Entry
R
Yield (%)
ee (%) (configuration)
1
Ph(CH
2
)
2
89
95
(R)
2
Me
2
COH
71
99
(R)
3
Me
2
COTMS
68
81
(R)
4
HO(CH
2
)
2
90
98
(R)
5
Et
3
Si
42
98
(R)
a)
Conditions: similar to Table 13.4, T
=
50 °C.
hydrochloride by reaction with 2,6-dipicolinic acid to give
49,
followed by treatment
with neat AcCl and base (Scheme 13.12).
HO
O
HO
OH
+
48
Cl
-
HO
NH
3
1) TMSCl, HMDS, py
2) 2,6-dipicolinic acid.HCl
3) MeOH-THF
65%
1) AcCl
2) Et
4
NCl, NaHCO
3
,
MeCN
O
O
OH
N
OH
O
O
N
O
O
NH
HN
N
N
O
O
42%
AcO
OAc
OH
HO
AcO
OAc
AcO
OAc
OH
OH
OH
OH
49
50
gluco
Pybox
Scheme 13.12
Synthesis of
gluco
Pybox ligand
50.
The catalytic system CuOTf/
gluco
Pybox afforded an excellent 99% ee and 69%
yield in the addition of phenylacetylene to imines (Table 13.6, entry 1). The cata-
lytic system appears to be very sensitive to the substituents R
1
-R
3
. Thus, for R
1
or
R
2
4-MeOPh, the ee decreased to 80 and 90%, respectively (entries 2 and 3). The
ee was also 90% when (trimethylsilyl)acetylene was used (R
3
=
TMS), although the
yield dropped significantly (entry 4). However, when substituents of the amino
and acetylene moieties were simultaneously modified racemic product was
obtained (entry 5). The ee values did not exceeded 75% when substituted benzal-
dehyde or aliphatic aldehydes were used (entry 6).
=
Search WWH ::
Custom Search