Chemistry Reference
In-Depth Information
O
b
a
c
O
OH
CN
CN
CN
101
102
103
104
d
e
h
f
g
OH
O
CHO
NC
NC
OH
NC
OH
O
CN
105
106
107
108
i
l
k
c
OH
O
NC
NC
NC
CO
2
Et
OHC
OH
110
109
112
113
j
m
k
steps
steps
NC
Cl
OHC
Cl
OHC
Cl
OH
111
97
3
97
Reagents and Conditions: (a) KN(TMS)
2
, (EtO)
2
POCH(CN)i-Pr, toluene,
78
C; (b) m-CPBA, CH
2
Cl
2
;
(c) Al(i-OPr)
3
, toluene; (d) EtOCH
¼
CH
2
, Hg(AcO)
2
; (e) 2,2-dimethoxy-2,3-dimethyl-butan-ol, 2 mol%
of 2,4-dinitrophenol, 130
C; (f) NaBH
4
, MeOH; (g) NaIO
4
, MeOH-H
2
O; (h) toluene, 110
C; (i) i. MsCl,
Py; ii. K
2
CO
3
, MeOH; (j) SOCl
2
, MeOH; (k) DIBAL-H toluene,
78
C; (l) Ph
3
P
¼
C(CH
3
)CO
2
Et,
CH
2
Cl
2
; (m) MsCl, LiCl, DMF.
Scheme 6-2
Macrocyclic ethers were obtained from a product of the ketal Claisen rearrange-
ment via baker's yeast reduction. A [2,3]-Wittig rearrangement of these compounds
afforded enantiomers of both sarcophytol A (3) and sarcophytol T (25) (in 1990)
with high enantioselectivity (91-98% ee) in high yields. Surprisingly, almost-
perfect reversal of chirality was observed between this geometrical isomer; that
is, (R)-ether gave (S)-alcohol as (2Z,4E) isomer, whereas it gave (R)-alcohol as
(2E,4Z)-isomer (Scheme 6-3).
Then Li et al. reported on a concise total synthesis of (
)-sarcophytol A (3) from
the derivative of E,E-farnesol (91) by a low-valent titanium-mediated intramolecu-
lar McMurry olefination strategy (Scheme 6-4).
83
6.4.1.2 Total Synthesis of Sarcophytol B
The first total synthesis of (
)-sarcophytol B (5) from E,E-farnesal (92), which
was reported by McMurry et al. in 1989, used a low-temperature titanium-induced
pinacol coupling reaction of 1,14-dialdehyde as the key step. They concluded that
the natural sarcophytol B has the stereochemistry of a trans diol (Scheme 6-5).
84
Li et al. reported on a concise total synthesis of (
)-sarcophytol B (5) from
E,E-farnesol (91) by a low-valent titanium-mediated intramolecular McMurry
Search WWH ::
Custom Search