The total synthesis of nyingchinoids Aa nd Bh as been achieved through successive rearrangements of a1 ,2dioxane intermediate that was assembled using av isible-light photoredox-catalysed aerobic [2+ +2+ +2] cycloaddition. Nyingchinoid Dw as synthesised with ac ompeting [2+ +2] cycloaddition. Based on NMR data and biosynthetic speculation, we proposed as tructure revision of the related natural product rasumatranin D, which was confirmed through total synthesis. Under photoredoxc onditions,w eo bserved the conversion of ac yclobutane into a1 ,2-dioxane through retro-[2+ +2] cycloaddition followed by aerobic [2+ +2+ +2] cycloaddition. Scheme 1. Proposed biosynthesis of nyingchinoidsA,
2,5-Bis(tert-butyldimethylsilyloxy)furans
are established as vicinal bisketene equivalents for application as
dienes in the Diels–Alder reaction. Cycloaddition with olefinic
dienophiles, under exceptionally mild conditions, enables convergent
access to highly substituted para-hydroquinones in
unprotected form via a one-pot Diels–Alder/ring-opening/tautomerization
sequence. The synthesis of para-benzoquinones from
acetylenic dienophiles, including benzynes, is also demonstrated,
and 2,5-bis(tert-butyldimethylsilyloxy)pyrroles
are established as competent dienes for the synthesis of para-iminoquinones. Application in natural product synthesis enables
gram-scale access to the neuroprotective agent (±)-indanostatin.
The field of biomimetic synthesis seeks to apply biosynthetic hypotheses to the efficient construction of complex natural products. This approach can also guide the revision of incorrectly assigned structures. Herein, we describe the evolution of a concise total synthesis and structural reassignment of hyperelodione D, a tetracyclic meroterpenoid derived from a Hypericum plant, alongside some biogenetically related natural products, erectones A and B. The key step in the synthesis of hyperelodione D forms six stereocentres and three rings in a bioinspired cascade reaction that features an intermolecular Diels–Alder reaction, an intramolecular Prins reaction and a terminating cycloetherification.
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<p>2,5-Bis(<i>tert</i>-butyldimethylsilyloxy)furans are established as masked vicinal bisketenes for application as dienes in
the Diels–Alder reaction. Cycloaddition with olefinic dienophiles, under exceptionally mild conditions, enables convergent access
to highly substituted <i>para</i>-hydroquinones in unprotected form via a one-pot Diels–Alder/ring-opening/tautomerization sequence.
The synthesis of <i>para</i>-benzoquinones from acetylenic dienophiles, including benzynes, is also demonstrated, and 2,5-bis(<i>tert</i>-butyldimethylsilyloxy)pyrroles are established as competent dienes for the synthesis of <i>para</i>-iminoquinones. Application in natural
product synthesis enables gram-scale access to the neuroprotective agent (±)-indanostatin.
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</div>
</div>
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The total synthesis of nyingchinoids A and B has been achieved through successive rearrangements of a 1,2‐dioxane intermediate that was assembled using a visible‐light photoredox‐catalysed aerobic [2+2+2] cycloaddition. Nyingchinoid D was synthesised with a competing [2+2] cycloaddition. Based on NMR data and biosynthetic speculation, we proposed a structure revision of the related natural product rasumatranin D, which was confirmed through total synthesis. Under photoredox conditions, we observed the conversion of a cyclobutane into a 1,2‐dioxane through retro‐[2+2] cycloaddition followed by aerobic [2+2+2] cycloaddition.
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