A highly enantioselective oxidative cyclopropanation of 1,6-enynes catalyzed by cationic Au(I)/chiral phophoramidite complexes is presented. The new method provides convenient access to densely functionalized bicyclo[3.1.0]hexanes bearing three contiguous quaternary and tertiary stereogenic centers with high enantioselectivity (up to e.r. 98:2). Control experiments suggest that the quinoline moiety of the β-gold vinyloxyquinolinium intermediate in the reaction plays an important role in promoting good enantioselectivity through a transitional auxiliary effect in the transition state.
Highly enantioselective gold-catalyzed intramolecular cyclization of N-allenamides was implemented by utilizing a designed chiral sulfinamide phosphine ligand (PC-Phos). This represents the first example of highly enantioselective intramolecular cyclization of N-allenamides. The practicality of this reaction was validated in the total synthesis of (R)-desbromoarborescidine A and formal synthesis of (R)-desbromoarborescidine C and (R)-deplancheine. Moreover, the catalyst system PC-Phos/AuNTf proved to be specifically efficient to promote the desymmetrization of N-allenamides in excellent yields with satisfactory ee values.
The discovery of catalytic systems based on earth-abundant
transition
metals for the functionalization of C–H bonds enables streamlined
and sustainable solutions to problems in synthetic organic chemistry.
In this Communication, we disclose an iron-based catalytic system
for the functionalization of propargylic and allylic C–H bonds.
Inexpensive and readily available cyclopentadienyliron(II) dicarbonyl
complexes were employed as catalysts for a novel deprotonative
activation mode for C–H functionalization, an approach that
allows for the direct union of unsaturated building blocks with aryl
aldehydes and other carbonyl electrophiles to deliver a range of unsaturated
alcohol coupling products under operationally simple and functional
group tolerant reaction conditions.
A highly enantioselective gold(I)-catalyzed intermolecular annulation of 2-(1-alkynyl)-2-alken-1-ones with N-allenamides is presented. The present work represents the first example of a gold-catalyzed annulation with the proximal C=C bond of an N-allenamide, and is distinctly different from the previously observed annulations at the distal C=C bond. Interestingly, both enantiomers of the products could be obtained in good yields with high regio-, diastereo-, and enantioselectivity by using either diastereomer of a binol-derived phosphoramidite as a chiral ligand.
A series of novel chiral monophosphine ligands Xiang-Phoses were designed and have been applied to the enantioselective gold-catalyzed intermolecular [2 + 2]-cycloaddition of 3-styrylindoles 1 with N-allenyl oxazolidinone 2.
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