The base-free benzoborirene 1,2-BR-1,2-C6H4 (7) and its three-dimensional inorganic
analogue 1,2-BR-1,2-C2B10H10 (13) have been successfully
synthesized by Cp2ZrBr2 and LiCl elimination,
respectively. The Cl analogue of the key intermediate for the formation
of benzoborirene 7 has been isolated and structurally
characterized, thus suggesting the reaction pathway via benzyne Zr
complex formation, B–Br/Cbenzyne–Zr σ-bond
metathesis, and a Cp2ZrBr2 elimination/ring-closing
process. The rationality of the reaction pathway has been confirmed
by DFT calculations. In addition, the title compounds shared the same
reactivity pattern (i.e., 1,3-silyl migration) toward MeIiPr (8), thus allowing for the synthetic
approach to the first carborane-substituted iminoborane 14.
By simple mixing of PhI(OAc)2, TmsCF3 and KF, a hypervalent iodine trifluoromethylating species is formed and directly applied in sp2 C—H trifluoromethylation reactions of ketene dithioacetals and indoles.
We report herein the catalytic triboration of terminal alkynes with B2pin2 (bis(pinacolato)diboron) using readily available Cu(OAc)2 and PnBu3. Various 1,1,2‐triborylalkenes, a class of compounds that have been demonstrated to be potential matrix metalloproteinase (MMP‐2) inhibitors, were obtained directly in moderate to good yields. The process features mild reaction conditions, a broad substrate scope, and good functional group tolerance. This copper‐catalyzed reaction can be conducted on a gram scale to produce the corresponding 1,1,2‐triborylalkenes in modest yields. The utility of these products was demonstrated by further transformations of the C−B bonds to prepare gem‐dihaloborylalkenes (F, Cl, Br), monohaloborylalkenes (Cl, Br), and trans‐diaryldiborylalkenes, which serve as important synthons and have previously been challenging to prepare.
This review summarizes new methodology for the synthesis of α-aminoboronates, including asymmetric synthetic methods and mechanistic explanations of reactivity. Applications of α-aminoboronates as versatile synthetic building blocks are also discussed.
A convenient and efficient one‐step synthesis of 1,1,1‐triborylalkanes was achieved via sequential dehydrogenative borylation and double hydroborations of terminal alkynes with HBpin (HBpin=pinacolborane) catalyzed by inexpensive and readily available Cu(OAc)2. This process proceeds under mild conditions, furnishing 1,1,1‐tris(boronates) with wide substrate scope, excellent selectivity, and good functional‐group tolerance, and is applicable to gram‐scale synthesis without loss of yield. The 1,1,1‐triborylalkanes can be used in the preparation of α‐vinylboronates and borylated cyclic compounds, which are valuable but previously rare compounds. Different alkyl groups can be introduced stepwise via base‐mediated deborylative alkylation to produce racemic tertiary alkyl boronates, which can be readily transformed into useful tertiary alcohols.
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