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Chem Asian J. 2019 Apr 15;14(8):1128-1135. doi: 10.1002/asia.201800903. Epub 2018 Aug 22.

Synthesis of the Bicyclic Lactone Core of Leonuketal, Enabled by a Telescoped Diels-Alder Reaction Sequence.

Author information

1
School of Chemical Sciences, University of Auckland, Symonds St, Auckland, 1010, New Zealand.
2
Maurice Wilkins Centre for Molecular Biodiscovery, University of Auckland, Symonds St, Auckland, 1010, New Zealand.

Abstract

The Diels-Alder cycloaddition reaction has become established as a fundamental approach for the preparation of complex natural products; however, successful application of the intermolecular Diels-Alder cycloaddition reaction to the synthesis of particularly congested scaffolds remains surprisingly problematic. Inspired by the terpenoid spiroketal natural product leonuketal, a challenging telescoped reaction sequence has been realized to access the core [2.2.2]-bicyclic lactone ring system and its [3.2.1] isomer. Our four-step, protecting-group-free process required detailed investigation to circumvent the problems of adduct fragmentation and intermediate instability. Successful solution of these practical issues, along with unambiguous structural determination of the target structures, provide useful insights that will facilitate future applications of the Diels-Alder cycloaddition reaction to challenging, highly congested molecular scaffolds and ongoing synthetic efforts towards this natural product.

KEYWORDS:

cycloaddition; leonuketal; multistep reactions; natural products; synthetic methods

PMID:
30058292
DOI:
10.1002/asia.201800903

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