A recent example of the use of dehydrative spirocyclization for the synthesis of a
heteroannulated spiroacetal natural product is Sudhakar et al.’s synthesis of the
acortatarins 37 and 38 [54] (Scheme 11).
Treatment of ketone 39 with PTSA resulted in deprotection of both the TBS and
THP ethers. Subsequent spirocyclization of the unmasked dihydroxyketone
afforded spiroacetals 40 and 41 as a mixture of anomers. Global deprotection
with TiCl 4 then gave the natural products 37 and 38 in good yield, along with
their spiro-epimers.
2.1.3 Bis(benzannulated) Spiroacetals
Dehydrative spirocyclization of a dihydroxyketone has also been successfully
applied to the synthesis of bis(benzannulated) spiroacetals. A recent example is
the total synthesis of paecilospirone 46 by Brimble et al. [55] (Scheme 12).
Scheme 11 Sudhakar et al.’s synthesis of acortatarins A and B [54]
Synthesis of 5,6- and 6,6-Spirocyclic Compounds
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