Scheme 4 of this Communication contains two typesetting mistakes that need to be corrected: 1) The text above the chemical formula for 9 a must read "g arylation" instead of "g arylation", and 2) the isomeric ratio for 14 a is "b/g > 98:2" and not "g/b > 98:2".
The direct functionalization of hydrocarbon chains represents a stepeconomical approach to tetrahedral carbon-rich functionalized organic intermediates from cheap and abundant feedstock, and has recently been a topic of intense investigations.[1] Two main strategies employing transition-metal catalysts have been pursued to tackle this challenging synthetic problem: [2] inner-sphere C-H activation, involving concerted C-H bond cleavage and carbon-metal bond formation, and outer-sphere C-H activation, not involving organometallic intermediates, which show distinct selectivity profiles. In most reported inner-sphere reactions, a directing group is employed to control the site-selectivity of the C-H bond cleavage, whereas non-directed methods are scarce.[1b] The transition metal-catalyzed C-H borylation reactions developed by Hartwig and co-workers constitute notable examples, wherein terminal-selective activation and functionalization of alkyl chains is achieved by steric control (Scheme 1a). [3,4] This borylation reaction can be followed by a Pd-catalyzed Suzuki-Miyaura cross-coupling in order to create a C-C bond at the same position (2 → 3), with the inconvenient that two noble metals are employed in this two-step sequence.[5] A conceptually different strategy is reported herein (Scheme 1b). Secondary bromoalkanes 4 are readily available compounds, which can be generated by bromination of abundant feedstock such as alkenes, alcohols, or even alkanes 1. The generation of an alkylzinc halide 5 from 4 by metal insertion, [6] followed by transmetallation to an in situ-generated organopalladium complex [Pd(R 2 )YL] would form the corresponding branched alkylpalladium intermediate 6. The latter would migrate to the terminal position (→ 7) via a succession of b-H elimination, rotation and insertion steps induced by a suitable ancillary ligand, where it would undergo reductive elimination to give the linear product 3. [7,8] Ligand-controlled Pd 0 -catalyzed migrative couplings have been investigated by our group using enolates as nucleophiles [9] or organozinc compounds obtained by Boc-directed lithiation and Li-Zn transmetallation.[10] In the current work, we show that terminal (linear) cross-coupling products 3 can be obtained in a regioconvergent manner in just one step from bromoalkanes 4 under operationally simple, Barbier (in situ) conditions. In addition, in most cases a similar selectivity pattern is obtained regardless of the position of the bromine atom in the alkyl chain. This observation led us to employ mixtures of bromides 4' obtained by radical bromination of linear alkanes 1. Indeed, this process is known to give rise to mixtures of secondary bromides, [11] and hence has been of little synthetic use so far. However, we reasoned that this mixture could be productively utilized by applying the same in situ metal insertion/migrative Negishi coupling sequence, wherein a mixture of branched organopalladium intermediates 6' would converge to the same linear complex 7,
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