Avenaol, isolated from the allelopathic plant black oat, was the first C20 germination stimulant related to strigolactones. Structurally, it consisted of a bicyclo[4.1.0]heptanone skeleton containing a cyclopropane ring bearing three main chains projecting in the same direction (i.e. all-cis-substituted cyclopropane). Herein, we report the total synthesis of avenaol using a robust strategy involving the formation of an all-cis-substituted cyclopropane via an alkylidenecyclopropane. The key factors in the success of this total synthesis include the Rh-catalysed intramolecular cyclopropanation of an allene, an Ir-catalysed stereoselective double-bond isomerisation, and the differentiation of two hydroxymethyl groups via the regioselective formation and oxidation of a tetrahydropyran based on the reactivity of a cyclopropyl group. This strategy effectively avoids the undesired ring opening of the cyclopropane ring and the formation of a caged structure. Furthermore, this study confirms the proposed structure of avenaol, including its unique all-cis-substituted cyclopropane moiety.
Caprazamycin A has significant antibacterial activity against Mycobacterium tuberculosis (TB). The first total synthesis is herein reported and features a) the scalable preparation of the syn-β-hydroxy amino acid with a thiourea-catalyzed diastereoselective aldol reaction, b) construction of a diazepanone with an unstable fatty-acid side chain, and c) global deprotection with hydrogenation. This report provides a route for the synthesis of related liponucleoside antibiotics with fatty-acid side chains.
Although acetalization is a fundamental transformation in organic synthesis, intermolecular asymmetric acetalization remains an unsolved problem. In this study, a thiourea‐ammonium hybrid catalyst was shown to promote the O‐alkylation of enols with a racemic γ‐chlorobutenolide through dynamic kinetic resolution to give chiral acetals with good enantioselectivity. The catalyst simultaneously activates both the nucleophile and electrophile in a multifunctional manner. This method was applied to the asymmetric synthesis of several strigolactones. DFT calculations suggest that hydrogen‐bonding interactions between the chlorine atom of the γ‐chlorobutenolide and the tosylamide hydrogen atom of the catalyst, as well as other types of noncovalent catalyst–substrate interactions, are crucial for achieving high stereoselectivity.
Copper-catalyzed
cycloisomerization of 3-iminocyclopropenes for
synthesis of pyrroles has been developed. The reaction allows regioselective
construction of pyrroles with various substitution patterns, including
fully substituted pyrroles. The method was successfully applied to
synthesis of steroidal pyrroles as well as a N-fused pyrrole.
The
first total synthesis of caprazamycin A (1), a
representative liponucleoside antibiotic, is described. Diastereoselective
aldol reactions of aldehydes 12 and 25–27, derived from uridine, with diethyl isocyanomalonate 13 and phenylcarbamate 21 were investigated using
thiourea catalysts 14 or bases to synthesize syn-β-hydroxyamino acid derivatives. The 1,4-diazepanone
core of 1 was constructed using a Mitsunobu reaction,
and the fatty acid side chain was introduced using a stepwise sequence
based on model studies. Notably, global deprotection was realized
using palladium black and formic acid without hydrogenating the olefin
in the uridine unit.
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