Department de Química Física i Inorgànica, Univ. Rovira i Virgili, C/Marcel.lí Domingo s/n, 43007 Tarragona, Spain.
Published: September 2013
AI Article Synopsis
Article Abstract
A rational approach towards the borylative ring-opening of vinylepoxides and vinylaziridines, by the in situ formed MeO(-)→bis(pinacolato)diboron adduct, has been developed. The enhanced nucleophilic character of the Bpin (sp(2)) moiety from the reagent favours the SN2' conjugated B addition with the concomitant opening of the epoxide and aziridine rings. The reaction proceeds with total chemoselectivity towards the polyfunctionalised (-OH or -NHTs) allyl boronate. Theoretical calculations have determined the transition states that come from the reaction of the vinylic substrates with the activated MeO(-)→bis(pinacolato)diboron adduct, and a plausible mechanism for the organocatalytic borylative ring opening reaction has been suggested.
State Key Laboratory of Coordination Chemistry, Chemistry and Biomedicine Innovation Center (ChemBIC), School of Chemistry and Chemical Engineering, Nanjing University, Nanjing, Jiangsu, China.
Recent strides in C-H borylation have significantly expanded our toolkit for the preparation of organoboronates. Nevertheless, avenues alternative to obtain these compounds via σ-C-C cleavage, thereby facilitating molecular scaffold editing, remain scarce. Several methodologies have been proposed for hydroboration of cyclopropanes by activating C-C bonds, conventionally relying on noble and hazardous metal catalysts to control reaction outcomes.
State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, China.
Chiral secondary alkyl amines with a vicinal quaternary stereocenter are undoubtedly important and ubiquitous subunits in natural products and pharmaceuticals. However, their asymmetric synthesis remains a formidable challenge. Herein, we merge the ring-opening 1,2-metallate shift with iridium-catalyzed enantioselective C()-H borylation of aziridines to deliver these frameworks with high enantioselectivities.
The application of cyclic diaryliodonium salts in the synthesis of bioactive natural product analogues was demonstrated. Axially chiral biaryls were obtained via the enantioselective ring opening of cyclic diaryliodonium salts. Regioselective borylation was key in accessing both enantiomers of a biphenol key intermediate in eight steps overall.
We report the copper-catalyzed borylation of unactivated vinylcyclopropanes to form six-membered cyclic borate salts. A copper complex bearing an N-heterocyclic ligand in combination with bis(pinacolato)diboron and LiOBu catalyzes the ring-opening of the substrate under mild reaction conditions. The protocol can be applied to aryl- and heteroaryl-substituted vinylcyclopropanes and can be conducted on a gram scale.
In contrast to the well-established oxidative C=C double bond cleavage to give the corresponding carbonyl compounds, little is known about reductive C=C double bond cleavage. Here we report that C-C single bond cleavage in 1,2-diaryl-1,2-diborylethanes proceeds by reduction with sodium metal to yield α-boryl benzylsodium species. In combination with our previous reductive diboration of stilbenes, the overall transformation represents reductive cleavage of the C=C double bonds of stilbene to yield α-boryl-α-sodiated toluenes.
