workup, and final oxidation with KMnO 4 /NaIO 4 ) gives the lower homologue 47
which reacts with two equivalents of MeLi to produce methyl ketone 48. Addition
of vinyl MgBr to this ketone provides a mixture of stereoisomeric allylic alcohols
49 that are converted into the corresponding bromides upon treatment with PBr 3
and pyridine. Their displacement with 7-hydroxycoumarin furnishes a 3:1 mixture
of rac-33 and its (Z)-stereoisomer [96].
The maneonenes 50 are tricyclic diethers found in the marine alga Laurencia
nidifica [97–99] (Fig. 6). Synthetic analogues like 54 have been prepared by
Renaud and Vionnet through radical addition to ketene acetal 51 (Scheme 7)
[100]. This generates radical 52 which isomerizes into 7-oxa-2-norbornyl radical
53. Allylic quenching of radical 53 with allyltributyltin produces tricyclic
compound 54.
Vetiver oil contains small amounts of ether 55 [101]. The Mediterranean marine
alga Laurencia obtusa has yielded 7-oxanorbornane 56 [102] and 7-oxanorbornene
57 [103]. The terpenoid 1,4-epoxy-6-eudesmanol has been isolated from Sideris
O
O
B r
H
Cl
3
6
12
(3Z,6S,12E): Maneonene A
(3E,6S,12Z): (E)-Maneonene B
(3Z,6S,12Z): (Z)-Maneonene B
(3Z,6R,12E): Maneonene C
50
Fig. 6 Maneonenes
O
COOH
O
HO
H
O
COOH
O
O
MgBr
OH
O
O
O
O
O
MeLi
HO
H
O
O
1) CH 2 N 2
2) PhMgBr
3) H 3 O
+
, D
4) KMnO 4 /NaIO 4
1) PBr 3 /Py
2) AcOH/K 2 CO 3
Acetone
rac-33 +
49
(Z)
+ 8-Hydroxycoumarine
CF 3 CO 3 H
CH 2 Cl 2
44
46
47
48
80%
45
43%
78%
38%
(5 steps)
Scheme 6 Synthesis of rac-farnesiferol-C
Synthesis of 7-Oxabicyclo[2.2.1]heptane and Derivatives
149
which reacts with two equivalents of MeLi to produce methyl ketone 48. Addition
of vinyl MgBr to this ketone provides a mixture of stereoisomeric allylic alcohols
49 that are converted into the corresponding bromides upon treatment with PBr 3
and pyridine. Their displacement with 7-hydroxycoumarin furnishes a 3:1 mixture
of rac-33 and its (Z)-stereoisomer [96].
The maneonenes 50 are tricyclic diethers found in the marine alga Laurencia
nidifica [97–99] (Fig. 6). Synthetic analogues like 54 have been prepared by
Renaud and Vionnet through radical addition to ketene acetal 51 (Scheme 7)
[100]. This generates radical 52 which isomerizes into 7-oxa-2-norbornyl radical
53. Allylic quenching of radical 53 with allyltributyltin produces tricyclic
compound 54.
Vetiver oil contains small amounts of ether 55 [101]. The Mediterranean marine
alga Laurencia obtusa has yielded 7-oxanorbornane 56 [102] and 7-oxanorbornene
57 [103]. The terpenoid 1,4-epoxy-6-eudesmanol has been isolated from Sideris
O
O
B r
H
Cl
3
6
12
(3Z,6S,12E): Maneonene A
(3E,6S,12Z): (E)-Maneonene B
(3Z,6S,12Z): (Z)-Maneonene B
(3Z,6R,12E): Maneonene C
50
Fig. 6 Maneonenes
O
COOH
O
HO
H
O
COOH
O
O
MgBr
OH
O
O
O
O
O
MeLi
HO
H
O
O
1) CH 2 N 2
2) PhMgBr
3) H 3 O
+
, D
4) KMnO 4 /NaIO 4
1) PBr 3 /Py
2) AcOH/K 2 CO 3
Acetone
rac-33 +
49
(Z)
+ 8-Hydroxycoumarine
CF 3 CO 3 H
CH 2 Cl 2
44
46
47
48
80%
45
43%
78%
38%
(5 steps)
Scheme 6 Synthesis of rac-farnesiferol-C
Synthesis of 7-Oxabicyclo[2.2.1]heptane and Derivatives
149