An unprecedented Fe(III)-catalyzed
Friedel–Crafts alkylation–hemiketalization–lactonization
cascade of electron-rich hydroxy arenes and distinctively functionalized
unsaturated 4-keto esters is developed for the construction of polycyclic
bridged 2-chromanol lactones. Following this simple and facile protocol,
a broad range of products was prepared in good to excellent yields
as a single diastereomer. An unusual conglomerate (enantiomerically
pure polymorph) of 3ac is reported along with the absolute
stereochemistry, and the remaining products were rigorously confirmed
by single-crystal X-ray analysis and analogy.
A unified and protecting-group-free
six-step total synthesis of bisabolane-type sesquiterpenoid beshanzuenone
D and its stereoisomers and abiespiroside A using S-(+)-carvone as a common chiral-pool building block is disclosed.
This synthetic route features chemoselective allylic chlorination
of carvone, Au(I)-catalyzed cycloisomerization induced construction
of furan from homopropargylic diol, substrate-controlled selective
hydroxylation using Davis-oxaziridine, and dye-sensitized photo-oxidation
(through 1O2) of hydroxyalkyl tethered furan
to access oxaspirolactone as key transformations. A comprehensive
set of NMR data along with DFT calculations, ECD spectra, and optical
rotation measurements of the synthesized beshanzuenone D and its epimers
were obtained to confirm absolute configurations.
Three novel furo-naphthoquinones,
enceleamycins A–C (1–3), and
a new N-hydroxypyrazinone
acid (4) were identified from the strain Amycolatopsis sp. MCC 0218, isolated from a soil sample collected from the Western
Ghats of India. Their chemical structure and absolute and relative
configurations were established by 1D and 2D NMR spectroscopy, single-crystal
X-ray crystallography, and high-resolution mass spectrometry. Compounds 1 and 3 were active against methicillin-susceptible
and -resistant Staphylococcus aureus with MIC values
of 2–16 μg/mL.
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