The highly enantioselective copper/chiral
phosphine-catalyzed hydro-,
bora-, and carbo-metalations of difluorocyclopropenes with PHMS [H-Si],
H-BPin, (BPin)2, and (CH3)2Zn [Zn-Me]
are shown to regiodivergently afford highly enantioenriched and functionalized
difluorocyclopropanes. These examples can be viewed as the first successful
syntheses of “chiral” gem-dimethyl
and tert-butyl analogues.
Optically active cyclopropanes have been widely investigated especially from the views of pharmaceutical and agrochemical industries, and substituting one of the methylenes with the difluoromethylene unit should be promising for developing novel biologically relevant compounds and functional materials. In this paper, the copper-catalyzed enantioselective hydrosilylation of gem-difluorocyclopropenes to provide the corresponding chiral gem-difluorocyclopropanes is presented. The use of copper(I) chloride, chiral ligands including bidentate BINAPs and monodentate phos-phoramidites, and silylborane Me 2 PhSi-Bpin accompanying sodium tert-butoxide in methanol was appropriate for the enantioselective hydrosilylation of the strained C=C double bond, and the resultant chiral difluorinated three-membered ring was unambiguously characterized. Subsequent activation of the silyl groups in enantio-enriched gem-difluorocyclopropanes showed substantial reduction of the enantiopurity, indicating cleavage of the distal CÀ C bond leading to the transient acyclic intermediates.
Gold‐catalyzed intermolecular reaction leading to dihydronaphthalene derivatives in one pot from two equivalents of ynones with respect to styrene is uncovered. The [4+2] Diels–Alder cycloaddition of ynones and styrenes is catalyzed by a mono‐gold(I) complex and the conjugated acid to provide an unstable 3,8a‐dihydronaphthalene to subsequently undergo an intermolecular ene‐type reaction with the π‐activated ynone to afford multi‐component coupling dihydronaphthalene products. Linear relationships between chiral ligand‐gold complexes and chiral dihydronaphthalene products proves mono‐gold catalysis that triggers an asymmetric tandem Diels–Alder and ene reaction sequence.
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