10.1002/chem.201800020
Chemistry - A European Journal
COMMUNICATION
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selective and enantioselective direct aldol reaction of α-vinyl
thioacetamide in hand, we devised a catalytic alternative to
access 6 using the aldol adduct 3lb obtained from the present
catalysis using corresponding aldehyde 1l and 2b. After
protection of the secondary hydroxyl group as a TBS ether, S-
methylation by MeOTf followed by hydrolysis with phosphate
buffer gave thioester 7, which was subjected to reduction with
LiBH4 to furnish primary alcohol 6a. According to the original
synthesis of blumiolide C,[6d] the 6a was converted to the
corresponding acrylate that engaged in ring-closing metathesis
using Grubbs 2nd-Gen catalyst to give unsaturated lactone 7a.[16]
Conjugate addition of the requisite C5 unit followed by removal of
the PMB group furnished reported intermediate 8, whose
spectroscopic data were in full accordance to those reported.
In summary, α-vinylated aldol donors were incorporated into
a direct aldol arsenal using thioamide chemistry. Enantioenriched
syn-β-hydroxy α-vinyl carboxylic acid derivatives are accessible
in a truly catalytic fashion. Further exploration of the synthetic
utility of the present catalysis is ongoing.
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Acknowledgements
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This work was financially supported by ACT-C (JPMJCR12YO)
from JST, and KAKENHI (17H03025, 17K08384, and
JP16H01043 in Precisely Designed Catalysts with Customized
Scaffolding) from JSPS and MEXT. Dr. Ryuichi Sawa, Ms.
Yumiko Kubota, and Dr. Kiyoko Iijima are gratefully
acknowledged for their assistance in spectroscopic analysis.
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a direct catalytic asymmetric aldol methodology using b,g-
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Keywords: aldol reaction • asymmetric catalysis • thioamide •
cooperative catalysis • formal synthesis
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