Barbier additions intermolecular

Curran described an efficient, approach to the BCD ring system of the penitrem indole alkaloids that exploits a Sml2-mediated radical-anionic sequence.11 Treatment of iodide 17 with Sml2 and HMPA gave 18, the product of radical cyclisation-intermolecular Barbier addition, in satisfactory yield (Scheme 6.6). 

Molander has also studied the Sml2-mediated double Barbier additions of alkyl dihalides to ketoesters.22,23 These impressive anionic-anionic, inter-molecular-intramolecular sequences require the use of Nil2 as an additive and irradiation with visible light and allow access to a range of bicyclic and tricyclic systems. The reactions proceed by reduction of the more reactive alkyl halide, intermolecular Barbier addition to the ketone, lactonisation and a second Barbier addition to the lactone carbonyl (Scheme 6.18).22... 

Additionally, various intra- and intermolecular iron-catalyzed Barbier-type reactions of organosamarium com-pounds and carbonyl electrophiles have been reported by Molander and co-workers. 

Although organosamariums can react with esters and lactones, they preferentially undergo addition to aldehydes or ketones. This allows organosamariums bearing an ester functionality to be generated and used in intermolecular Barbier couplings (Scheme 5.74).98,99... 

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