7 Ring-Opening of Bicyclic Substrates
Oxabicyclic substrates are attractive precursors to tetrahydrofurans as a consequence
of the ease with which they are synthesized and that they lead to the exclusive
generation of 2,5-cis-tetrahydrofurans. Included in this section is one example of an
enzymatic approach to tetrahydrofurans from an oxabicyclic ring system and several
examples of ring-opening metathesis approaches to tetrahydrofurans.
O
N
+
R'O
O
Cl
Et 3 N, PhCH 3
O
N
RO
O
rt
80%
H 2 C CH 2 , CH 2 Cl 2 , rt
Cl 2 (PCy) 2 Ru=CHPh (10 mol %)
O
N
OR
O
85%
224
(R' = Ph, Bn)
223
225
227
226
Scheme 60 ROM/RCM approach to spiro-fused tetrahydrofurans by Plumet et al. [68]
Ru
H
N
N
Cl
Cl
PCy3
Mes
Mes
Ph
229
229 (30 mol %)
CH 2 Cl 2 , rt
BnN
CH 2 CH 2
95%
O
N
Boc
228
230
O
O
N
Bn O
N
Boc
Scheme 61 ROM/RCM to fused tetrahydrofurans by Winkler et al. [69]
O
O
R
Cl 2 (PCy 3 ) 2 Ru=CHPh (226) (5 mol %)
CH 2 Cl 2 , rt
O
O
R
(R = H) (88%)
(R = Me) (79%)
O
O
R
226 (10 mol %)
CH 2 Cl 2 , rt
O
O
R
O
R
O
R
231
232
(R = H) (85%)
(R = Me) (93%)
234
233
Scheme 62 Enyne metathesis route to polycyclic tetrahydrofurans by Plumet et al. [70]
Synthesis of Substituted Tetrahydrofurans
29