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H
H
O
O
O
N
N
b,c
a
+
O
O
O
O
O
O
3
(85:15)
Bn
OMe
N
O
N
OMe
N
d,e
g
f
O
O
O
H
O
O
O
OMe
2a
Me
Me
Me
HO
N
N
OMe
N
OMe
h
i
OMe
COOMe
O
COOMe
COOMe
O
4
Me
Me
N
N
j
OMe
k
l
OMe
(±)-HA
COOMe
NHCO
2
Et
5
Reagents:
a). Pyrrolidine, PhH, p-TsOH (catalyst), reflux; acrylamide, dioxane, reflux; H
2
O,
dioxane, reflux (70% overall); b). KH, BnCl, THF, rt (100%); c) LDA, PhSeCl, THF, -78
°C;
NaIO
4
; Et
3
N, MeOH, Reflux (80%); d) H
2
, Pd(OH)
2
/C, HOAc, rt (80%); e) Ag
2
CO
3
, MeI,
CHCl
3
, rt (92%); f) 5% HCl, acetone, reflux (85%); KH, (MeO)
2
CO, reflux (87%);
g) methacrolein, tetramethylguanidine, CH
2
Cl
2
, rt (93%);
h) MsCl, Et
3
N, DMAP, CH
2
Cl
2
(96%); NaOAc, HOAc, 110
C, 24 h (50%);
i) Ph
3
P=CHCH
3
, THF, 0 °C to rt (73%); j) PhSH, AIBN, 170 °C, 24h (100%);
k) 20% NaOH, THF, MeOH, reflux, 2 days (78% based on E ester); SOCl
2
, toluene, 80 °C, 2h;
NaN
3
, 80 °C; MeOH, reflux (80% overall); l) TMSI, CHCl
3
, reflux (92%).
°
Scheme 4-2. Synthetic approaches to (
)-HA by Xia and Kozikowski.
H
OMe
N
O
O
N
a
O
H
O
O
O
O
O
OMe
3
6
2a
Reagents and conditions: a). methyl propiolate, NH
3
, MeOH, 100
°
C, 10 h (70%)
Scheme 4-3. One-pot process to prepare 6.
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