2.13 Intramolecular Hydrogen Abstraction (IHA)
for the Synthesis of Spiroacetals
The application of this method (Scheme 86) in the syntheses of a variety of
spiroacetal natural products has been reviewed recently [175]. The mild reaction
conditions enable construction of spiroacetals from very sensitive substrates that
would not withstand more classical spirocyclization strategies (e.g., acid-catalyzed
dehydrative spirocyclization).
Formation of five-membered rings using this method is favored over
six-membered rings due to the relative stabilities of the six- and seven-membered
Scheme 83 Furan oxidation approaches toward crassalactone D and pyrenolide D [172, 173]
Scheme 84 Robertson et al.’s furan oxidation approach toward the sawaranospirolides [141]
Synthesis of 5,6- and 6,6-Spirocyclic Compounds
247
for the Synthesis of Spiroacetals
The application of this method (Scheme 86) in the syntheses of a variety of
spiroacetal natural products has been reviewed recently [175]. The mild reaction
conditions enable construction of spiroacetals from very sensitive substrates that
would not withstand more classical spirocyclization strategies (e.g., acid-catalyzed
dehydrative spirocyclization).
Formation of five-membered rings using this method is favored over
six-membered rings due to the relative stabilities of the six- and seven-membered
Scheme 83 Furan oxidation approaches toward crassalactone D and pyrenolide D [172, 173]
Scheme 84 Robertson et al.’s furan oxidation approach toward the sawaranospirolides [141]
Synthesis of 5,6- and 6,6-Spirocyclic Compounds
247