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.

Addition of alkyl radicals generated from B-alkylcatecholboranes onto 1,4-benzoquinones leads to substituted hydroquinones in good overall yields. Formation of aryl ethers via a unique radical addition to the oxygen atom of the enone system is the main reaction when bulky secondary and tertiary alkyl radicals are used. Less hindered secondary and primary radicals give the expected 1,4-conjugate addition products. [reaction: see text]

A one-pot procedure for the efficient hydroazidation of alkenes involving hydroboration with catecholborane followed by reaction with benzenesulfonyl azide in the presence of a radical initiator is described. The regioselectivity is controlled by the hydroboration step and corresponds in most cases to an anti-Markovnikov regioselectivity. This procedure is applicable to a wide range of alkenes and gives excellent results with 1,2-disubstituted and trisubstituted alkenes.

An efficient formal anti-Markovnikov addition of HX (X = Cl, Br, I, SR and SeR) to olefins under mild reaction conditions is described. The procedure is based on the hydroboration of alkenes with catecholborane. The conversion of the intermediate B-alkylcatecholboranes to the corresponding halides, sulfides and selenides is based on a common process, i.e., generation of a radical from the alkylborane followed by abstraction of a heteroatom from an aromatic sulfonyl reagent. The efficiency of these radical reactions is remarkable. The mildness of the reaction conditions is well illustrated by the preparation of iodoalkanes. Despite the notorious reactivity of iodoalkanes under radical reaction conditions, no product degradation was observed.

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.

[reaction: see text] A new class of N-substituted radical has been studied. Obtained from the corresponding chlorides, beta-lactamido N-sulfonyl radicals were allylated and added onto electron-rich olefins. It has been shown that the radicals do not undergo desulfonylation and are electrophilic in nature.

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Radical reactions O 0195An Efficient Radical Procedure for the Halogenation and Chalcogenation of B-Alkylcatecholboranes. -The procedure allows even the preparation of iodoalkanes without any degradation despite of radical conditions. -(SCHAFFNER, A.-P.; MONTERMINI, F.; POZZI, D.; DARMENCY, V.; SCANLAN, E. M.; RENAUD*, P.; Adv. Synth. Catal. 350 (2008) 7-8, 1163-1167; Inst. Chem. Biochem., Univ. Bern, CH-3012 Bern, Switz.; Eng.) -Nuesgen 39-034