Nitrogen heterocycles
(azacycles) are common structural motifs
in numerous pharmaceuticals, agrochemicals, and natural products.
Many powerful methods have been developed and continue to be advanced
for the selective installation and modification of nitrogen heterocycles
through C–H functionalization and C–C cleavage approaches,
revealing new strategies for the synthesis of targets containing these
structural entities. Here, we report the first total syntheses of
the lycodine-type
Lycopodium
alkaloids casuarinine
H, lycoplatyrine B, lycoplatyrine A, and lycopladine F as well as
the total synthesis of 8,15-dihydrohuperzine A through bioinspired
late-stage diversification of a readily accessible common precursor,
N
-desmethyl-β-obscurine. Key steps in the syntheses
include oxidative C–C bond cleavage of a piperidine ring in
the core structure of the obscurine intermediate and site-selective
C–H borylation of a pyridine nucleus to enable cross-coupling
reactions.
A new and facile one-pot synthesis of 1,3-disubstituted allenes, using cheap and readily available terminal alkynes, benzaldehyde derivatives and morpholine, was developed. A small library of 20 allenes demonstrates a broad applicability, with yields up to 86%. Isotopic-labelling and cross-over experiments strongly indicate that our reaction proceeds via a two-step A 3 -coupling followed by a 1,5-hydrogen shift process.
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