2.3 Acid-Catalyzed Spirocyclization of a Hemiacetal
Dehydrative spirocyclization may also be performed on hemiacetals, whereby
treatment with a Brønsted or Lewis acid gives rise to an oxonium ion intermediate.
Subsequent attack of the pendant alcohol thus affords the spiroacetal (Scheme 21).
In their studies toward the avermectin 2b spiroacetal 81, Henryon and Fe ´re ´zou
[67] have utilized an acid-catalyzed spirocyclization of hemiacetal 80 (Scheme 22).
Scheme 19 Borrero and Aponick’s Pd-catalyzed spirocyclization approach toward acortatarin A
[64]
Scheme 20 Cossy et al.’s Fe(III)-catalyzed spirocyclization approach [65, 66]
Synthesis of 5,6- and 6,6-Spirocyclic Compounds
205
Dehydrative spirocyclization may also be performed on hemiacetals, whereby
treatment with a Brønsted or Lewis acid gives rise to an oxonium ion intermediate.
Subsequent attack of the pendant alcohol thus affords the spiroacetal (Scheme 21).
In their studies toward the avermectin 2b spiroacetal 81, Henryon and Fe ´re ´zou
[67] have utilized an acid-catalyzed spirocyclization of hemiacetal 80 (Scheme 22).
Scheme 19 Borrero and Aponick’s Pd-catalyzed spirocyclization approach toward acortatarin A
[64]
Scheme 20 Cossy et al.’s Fe(III)-catalyzed spirocyclization approach [65, 66]
Synthesis of 5,6- and 6,6-Spirocyclic Compounds
205