Catalytic Asymmetric Hydroboration: Recent Advances and Applications in Carbon−Carbon Bond‐Forming Reactions

The iron pincer complex (IPC) is found to be optimal as precatalyst in the transformation of various alkenes.

Iron‐Catalyzed, Atom‐Economical, Chemo‐ and Regioselective Alkene Hydroboration with Pinacolborane

An extremely efficient cobalt catalyst for the hydroboration of both vinylarenes and aliphatic α-olefins with pinacolborane is described, providing the anti-Markovnikov products with excellent regio- and chemoselectivity, broad functional-group tolerance, and high turnover numbers (up to 19,800). The alkene hydroboration route is further extended to a two-step, one-pot hydroboration and cross-coupling of alkylboronates with aryl chlorides.

A Cobalt-Catalyzed Alkene Hydroboration with Pinacolborane†

Catalyst-free dehydrocoupling of amines, alcohols, and thiols with pinacol borane and 9-borabicyclononane (9-BBN)

The addition of Lewis acids such as trispentafluoroboron as cocatalysts has been found to have a dramatic effect on the Rh-catalyzed hydroboration of olefins with pinacol borane. For example, aliphatic olefins do not react at all in noncoordinating solvents, but with the addition of 2% of B(C6F5)3, the reaction is complete in minutes. Similarly, the reaction of aromatic olefins with HBPin occurs slowly and nonselectively in the absence of B(C6F5)3, but is accelerated and occurs more selectively in its presence. Preliminary mechanistic studies suggest that the B(C6F5)3 needs to be present throughout the course of the reaction, not just at the initiation stage, and implicate this species, along with THF, in the heterolytic cleavage of the B−H bond of HBPin.

Dramatic effect of Lewis acids on the rhodium-catalyzed hydroboration of olefins.

The in situ rhodium-catalyzed addition of catecholborane (HBcat, cat = 1,2-O2C6H4) and pinacolborane (HBpin, pin = 1,2-O2C2Me4) to allylamine, allylimine, 2- and 4-vinylpyridines, and a thienyl imi...

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Rhodium-catalyzed hydroborations of allylamine and allylimines

An α-ester disulfide is shown to be a useful precursor for the preparation of several α-sulfone disulfides. These new α-sulfone disulfides are all fungitoxic against Aspergillus niger and Aspergillus flavus. RSO2CH2SSCH9

A New Synthesis for Antifungal α-Sulfone Disulfides

Previously identified classes of antifungal disulfides are modified by extending alkyl substituents. Although, the principal focus is on f -sulfone disulfides, one nitrophenyl alkyl disulfide and a pair of f -ester disulfides were also prepared and examined. Optimum fungitoxicity is associated with structures which have seven to ten carbon atoms in the form of unbranched chains and/or phenyl rings.

Optimizing disulfide fungitoxicity: Adjustment of hydrocarbon chain length

Recently developed synthetic methodology has been exploited for the preparation of an assortment of α,α´-disubstituted disulfides including all three linkage isomeric types of α,α´-diester dimethyl disulfides. Two of the diesters are very powerful antifungal agents against Aspergillus niger and Aspergillus flavus. An α-ester α´-sulfone disulfide is the most powerful fungitoxin developed by this ongoing research effort.

Paul Eric O'Connor

Papers

Rhodium-catalyzed hydroborations of allylamine and allylimines

A New Synthesis for Antifungal α-Sulfone Disulfides

Optimizing disulfide fungitoxicity: Adjustment of hydrocarbon chain length

Selected a,a'-Dimethyl Disulfides: Submicrogram Fungitoxins

A New Synthesis for Antifungal α‐Sulfone Disulfides.