Chemistry Reference
In-Depth Information
OMe
OMe
BnO
Me
BnO
Me
TBSO
AcO
H
TBSO
HO
H
H
guanidinium nitrate (
4
)
H
Me
Troc
Me
N
Troc
N
NaOMe, MeOH-CH
2
Cl
2
40 °C
N
N
O
H
O
H
H
AcO
O
O
H
HO
85%
O
O
97
98
HO
OMe
NH
HO
Me
MeO
O
S
AcO
H
H
O
Me
NMe
N
O
H
O
OH
ecteinascidin 743 (
99
)
Scheme 7.20
Synthesis of ecteinascidin 743 (99)
Futagami et al. synthesized ent-ravidomycin (115) [35]. In the final stage of the
synthesis, DBN was used for the simultaneous removal of acetate protection of a phenolic
hydroxyl group and elimination of mesylate to give 115 (Scheme 7.25).
Hughes et al. achieved a synthesis of amythiamicin D (121) using a biosynthesis inspired
hetero Diels-Alder reaction as a key step [36]. Synthesis of the key 1-alkoxy-2-azadiene
118 was conducted by coupling of the imidate 116 and amine hydrochloride 117 and
subsequent elimination of the acetate with DBU [37]. The hetero Diels-Alder reaction of
the azadiene 118 and enamide 119 proceeded under microwave conditions to give the
pyridine 120, which was effectively converted into the natural product 121 (Scheme 7.26).
Synthesis of oxazoles and thiazoles from corresponding oxazolines and thiazolines by
dehydrogenation using the bromotrichloromethane (BrCCl
3
)-DBU systemwas reported by
Williams et al. [38]. This transformation was applied to synthesize many natural products.
Doi and Takahashi reported the synthesis of telomestatin (124) [39], which has a
macrocyclic polyoxazole structure. Reaction of oxazoline 122 with BrCCl
3
-DBU gave
trisoxazole 123 (Scheme 7.27). This left-hand segment was employed for the synthesis of
telomestatin 124.
Vinyl halide is a useful synthetic intermediate for natural products. Knapp et al. reported
the synthesis of griseolic acid B (130) via intramolecular radical cyclization of vinyl iodide
[40]. Aldehyde 125 was reacted with hydrazine to give hydrazone 126, which was further
