Boron derivatives are becoming key reagents in radical chemistry. Here, we describe reactions where an organoboron derivative is used as a radical initiator, a chain-transfer reagent, and a radical precursor. For instance, B-alkylcatecholboranes, easily prepared by hydroboration of alkenes, represent a very efficient source of primary, secondary, and tertiary alkyl radicals. Their very high sensitivity toward oxygen-and heteroatom-centered radicals makes them particularly attractive for the development of radical chain processes such as conjugate addition, allylation, alkenylation, and alkynylation. Boron derivatives have also been used to develop an attractive new procedure for the reduction of radicals with alcohols and water. The selected examples presented here demonstrate that boron-containing reagents can efficiently replace tin derivatives in a wide range of radical reactions.

Amino acid derived nitrones were conveniently synthesized in good-to-excellent yields by condensation of alpha-ketoesters with N-benzylhydroxylamine. The cycloaddition reactions of these nitrones with different alkenes were investigated under thermal solvent-free conditions. Considering conversions, yields, and selectivities, alkyl vinyl ethers have proven to be valuable partners to achieve this transformation, which creates a tetrafunctionalized stereogenic quaternary center. From the adducts derived from vinyl ethers, a three-step access to highly functionalized alpha-substituted amino acid derivatives is described.

A one-pot procedure involving radical conjugate addition of B-alkylcatecholboranes to enones followed by intramolecular aldol reaction is reported. Application to the stereoselective synthesis of monocyclic and bicyclic products with up to four contiguous stereogenic centers is presented.

International audienc

Boron derivatives are becoming key reagents in radical chemistry. Here, we describe reactions where an organoboron derivative is used as a radical initiator, a chain-transfer reagent, and a radical precursor. For instance, B-alkylcatecholboranes, easily prepared by hydroboration of alkenes, represent a very efficient source of primary, secondary, and tertiary alkyl radicals. Their very high sensitivity toward oxygen-and heteroatom-centered radicals makes them particularly attractive for the development of radical chain processes such as conjugate addition, allylation, alkenylation, and alkynylation. Boron derivatives have also been used to develop an attractive new procedure for the reduction of radicals with alcohols and water. The selected examples presented here demonstrate that boron-containing reagents can efficiently replace tin derivatives in a wide range of radical reactions.

Chiral phosphoric-acid-catalyzed asymmetric reductions of trans-chalcones have been investigated in this work. A BINOL-derived boro-phosphate-catalyzed asymmetric transfer hydrogenation of the carbon–carbon double bond of trans-chalcone derivatives employing borane as a hydride source was realized. This methodology provides a convenient procedure to access chiral dihydrochalone derivatives in high yields and with high enantioselectivities under mild conditions.

Heavy silyl enol ethers (mostly TIPS and TBS) combine with cyclic N-alkenyl N-acyliminium salts generated in situ from their N,O-acetal precursors, to furnish highly functionalized indolizidines through an unprecedented double Mukaiyama-Mannich-Prins cascade transformation. This novel cascade annulation process demonstrates a promising scope, and takes place mostly catalytically with interesting stereocontrol. Furthermore, an appealing facet of this chemistry is emphasized with a bicatalytic approach by which the Mannich-Prins cascade follows a Ru-catalyzed N-allylamide to N-(E)-propenyl isomerization of the aminal counterpart in a one-pot operation.

No abstract