8.2 14-Membered Macrocyclic Lactones
8.2.1 Aspergillide A and B
Oxidation of 117 with Dess–Martin periodinane and a subsequent
Masamune–Roush [75] modified intramolecular Horner–Wadsworth–Emmons
(HWE) reaction gave the 14-membered macrolactone 118 in 78 % yield over two
steps [76] (Scheme 30).
8.3 16-Membered Macrocyclic Lactones
8.3.1 (+)-Rhizoxin D
Using the Masamune–Roush protocol [75] for base-sensitive substrates, the intramolecular Horner–Wadsworth–Emmons (HWE) coupling reaction established the
macrocyclic C2–C3 bond in 80 % yield [77] (Scheme 31).
9 Stille and Stille-Type Transformations in Macrolactone
Formation
Another frequently employed approach to establish ring closure is to use palladium
mediated cross-coupling reactions. Among these, the Stille coupling is considered
to be a promising protocol since the double-bond geometry can be established prior
to the C–C bond formation and vinyl or aryl halides and stannanes are easily
accessible and tolerate a variety of subsequent transformations.
Scheme 30 Intramolecular HWE reaction in the total synthesis of aspergillide A, 119 and
aspergillide B, 120
394
M. Cordes and M. Kalesse
8.2.1 Aspergillide A and B
Oxidation of 117 with Dess–Martin periodinane and a subsequent
Masamune–Roush [75] modified intramolecular Horner–Wadsworth–Emmons
(HWE) reaction gave the 14-membered macrolactone 118 in 78 % yield over two
steps [76] (Scheme 30).
8.3 16-Membered Macrocyclic Lactones
8.3.1 (+)-Rhizoxin D
Using the Masamune–Roush protocol [75] for base-sensitive substrates, the intramolecular Horner–Wadsworth–Emmons (HWE) coupling reaction established the
macrocyclic C2–C3 bond in 80 % yield [77] (Scheme 31).
9 Stille and Stille-Type Transformations in Macrolactone
Formation
Another frequently employed approach to establish ring closure is to use palladium
mediated cross-coupling reactions. Among these, the Stille coupling is considered
to be a promising protocol since the double-bond geometry can be established prior
to the C–C bond formation and vinyl or aryl halides and stannanes are easily
accessible and tolerate a variety of subsequent transformations.
Scheme 30 Intramolecular HWE reaction in the total synthesis of aspergillide A, 119 and
aspergillide B, 120
394
M. Cordes and M. Kalesse