Plumet and coworkers successfully carried out ring-opening, ring-closing enyne
metathesis reactions to give bicyclic and tricyclic tetrahydrofuran derivatives
[70]. For example, the ring-opening and ring-closing enyne metathesis of 231
resulted in the generation of bicyclic derivative 232. In a similar fashion, the
reaction of oxanorbornene 233 gave tricyclic tetrahydrofuran 234 (Scheme 62).
O
R 1
R 2
S Ar
O
O
S(O)Ar
TBSOTf, 2,6-di-t-BuPy
R 1
R 2
MeOH, Et 3 N
oxone
O
SO 2 Ar
R 1
R 2
Ar = 4-chlorophenyl
R, 256 (2.5 to 10 mol %)
O
Ts
R
Ru
N
N
Cl
Cl
O
Mes
Mes
256
90-98% (2 steps)
H 3 C
CH 3
R
1
, R
2 = CH 3
55-94%
(R = CH 2 TMS, Ph, CH 2 Ph, CH 2 OAc, n-Bu, H)
252
253
254
255 (endo/exo = 1.8:1 to 25:1)
257
(de = 98%)
ClCH 2 CH 2 Cl, 0 °C or 25 °C
Scheme 67 Optically active 7-oxanorbornenes in ROCM reactions by Martin and Benjamin [73]
Br
CHO
MeO
MeO
O
B(OH)2
(PPh 3 ) 2 PdCl 2 (10 mol %)
2 M Cs 2 CO 3 , THF
66 °C
CHO
MeO
MeO
O
Ph 3 =CH 2 Br
n-BuLi, THF
0 °C
MeO
MeO
O
MeO 2 C
CO 2 Me
PhH, 40 °C
72%
MeO
MeO
O
CO2Me
MeO 2 C
55%
Ru
H
N
N
Cl
Cl
PCy 3
Mes
Mes
Ph
229
229 (10 mol %)
CH 2 Cl 2 , 35 °C
MeO
MeO
O
MeO 2 C
MeO 2 C
H
MeO
MeO
O
O
OH
OH
O
O
OH
OH
O
O
Phelligridin G
258
259
260
261
262
263
50%
Scheme 68 ROM/RCM approach to the Phelligridin G scaffold by Cooper and Wright [74]
32
J.D. Rainier