Pd-Catalyzed Borylative Polycyclization of Enediynes to Alkylboronates

Rh-Catalyzed Borylative Cyclization of Acrylate-Containing 1,6-Enynes

A Rh-catalyzed regioselective, stereoselective carbocyclization/borylation of acrylate-containing 1,6-enynes was described, which offers a general and practical method for constructing versatile and densely functionalized pyrrolidines with the (Z) geometry or the uncommon (E) geometry at the double bond with different substituents of the alkyne, with sterically hindered and conjugative aryl groups favoring the latter, featuring a tetrasubstituted vinyl boronate, containing an all-carbon quaternary stereocenter.

Borylative Cyclization of 1,6-Allenynes Driven by BCl3

A metal-free intramolecular borylative cyclization of 1,6-allenynes driven by BCl₃ was developed. This method provides a general and practical strategy to construct valuable pyrrolidines containing all-carbon quaternary centers or 3,5-dihydroazepine derivatives depending on the substituents of the allene, with conjugative and sterically hindered phenyl groups favoring the latter.

Atom-Economical Ni-Catalyzed Diborylative Cyclization of Enynes: Preparation of Unsymmetrical Diboronates

We report a Ni-catalyzed diborylative cyclization of enynes that affords carbo- and heterocycles containing both alkyl- and alkenylboronates. The reaction is fully atom-economical, shows a broad scope, and employs a powerful and inexpensive catalytic Ni-based system. The reaction mechanism seems to involve activation of the enyne by Ni(0) through oxidative cyclometalation of the enyne prior to diboron reagent activation. An unprecedented dinuclear bis(organometallic) Ni(I) intermediate complex was isolated.

Atom-economical regioselective Ni-catalyzed hydroborylative cyclization of enynes: development and mechanism

We report a full study on the novel regioselective Ni-catalyzed hydroborylative cyclization of enynes using HBpin as the borylation agent.

Iron-Catalyzed Hydroborylative Cyclization of 1,6-Enynes

We report first Fe-catalyzed hydroborylative cyclization reaction. The process provides one C-C and one C-B bond in a single operation and shows a wide scope, allowing the formation of carbo- and heterocycles containing a homoallylic boryl unit that can be further functionalized. The reaction takes place in smooth conditions, with inexpensive catalytic system and full atom economy since HBpin is the borylation agent, in contrast to our previously reported Pd-catalyzed reaction. Both aryl and alkyl substituted alkynes are reactive, revealing a wide reaction scope. Mechanistic studies suggest the intermediacy of Fe^II -hydride active catalyst capable to react with the alkyne group prior to alkene insertion, and computational studies suggest the occurrence of barrierless σ-bond metathesis involving HBpin and Fe-C bonds along the catalytic cycle.

Formal nucleophilic borylation and borylative cyclization of organic halides

Recent advances in borylations of organic halides, including both transition-metal-catalyzed and metal-free methods are summarized. Borylative cyclization is also discussed.

Diboron(4) Compounds: From Structural Curiosity to Synthetic Workhorse

Although known for over 90 years, only in the past two decades has the chemistry of diboron(4) compounds been extensively explored. Many interesting structural features and reaction patterns have emerged, and more importantly, these compounds now feature prominently in both metal-catalyzed and metal-free methodologies for the formation of B-C bonds and other processes.

Cyclopropanation/Carboboration Reactions of Enynes with B(C6F5)3

Stoichiometric reaction of B(C6F5)3 with 1,6-enynes is shown to proceed via initial cyclopropanation and formal 1,1-carboboration. Depending on the substitution on the alkene moiety, subsequent ring-opening of the cyclopropane affords either cyclopentane or cyclohexane derivatives in which the C6F5 and B(C6F5)2 adopt a 1,4-positioning. Mechanistically, this transformation involves π-activation of the alkyne moiety, which triggers cyclopropanation, followed by carboboration. Both the cyclopropanation and subsequent ring-opening are shown to be stereospecific. Both cyclopropanation and 1,4-carboborated products were employed as Lewis acid components in frustrated Lewis pair activation of H2 and CO2.

Ligand-controlled divergent formation of alkenyl- or allylboronates catalyzed by Pd, and synthetic applications

Pd-catalysed reactions of allyl carbonates containing alkynes with B2(pin)2 afford either alkenylboronates by cascade borylative cyclisation, or allylboronates. The reaction outcome is controlled by a suitable choice of ligands. Boronates have been applied to a number of synthetic applications.