Chemistry Reference
In-Depth Information
high yields (82-86%) as the single, conformationally most stable diastereoisomer under
standard PKR conditions (i.e., the Co
2
CO
8
-NMO system) (Scheme 4.28).
O
(1
R
-(+)-Camphor
Propargylbromide/
Mg, HgCl
2
,dry ether
(78%)
Allylbromide/
Mg, dry ether
(89%)
3-bromo-2-methylpropene/
Mg, dry ether
(87%)
OH
OH
OH
(-)-
103c
(+)-
103a
(+)-
103b
KH, TMS-propargylbromide/
TBAI, THF (80%)
KH, TMS-propargylbromide/
TBAI, THF (75%)
KH, 3-bromo-2-methylpropene/
THF, TBAI (78%)
KH, allylbromide, TBAI/
THF (82%)
O
O
O
O
(+)-
104a
(+)-
104b
(-)-
105a
(-)-
105b
Co
2
(CO)
8
,NMO/
DCM (85 %)
Co
2
(CO)
8
,NMO/
DCM (82 %)
Co
2
(CO)
8
,NMO/
DCM (82 %)
Co
2
(CO)
8
,NMO/
DCM 86 %)
O
O
O
CH
3
O
H
O
O
O
O
H
3
C
H
(+)-
106a
(+)-
106b
(-)-
107a
(-)-
107b
O
O
R
O
R
O
106
107
R = H, CH
3
R = H, CH
3
Scheme 4.28
Simple route to synthesis camphor-anchored achiral spiro cyclopentenone-
pyran systems.
In 2008, Verdaguer and Riera
et al.
reported a new enantioselective approach to various
carbanucleosides from chiral cyclopentenone
108
via Pauson-Khand reaction.
31
Multigram
quantities of
108
were obtained in good yield (53%) with excellent enantiomeric purity
(
99%) via a PKR involving trimethylsilylacetylene, Co
2
(CO)
8
, and norbornadiene with
N
-benzyl-
N
-diphenylphosphino-
tert
-butyl-sulfinamide as a chiral P,S ligand, as previously
described by the same authors.
32
Next, a hydroxymethyl group was efficiently added to PK
cycloadduct
108
via photochemical conjugate addition. Protection using a triisopropylsilyl
