Manganese, Reformatsky reactions

Scheme 5.86 Cozzi s enantioselective Reformatsky reaction, mediated by manganese salen complex 313.

Manganese metal (commercial quality) without any special preparation allows Barbier or Reformatsky reactions, respectively, to be performed from allylic bromides and a-halogenoesters. The use of manganese is of real preparative interest since these reactions have a large scope of application and occur under mild conditions to give high yields of 1,2-addition products (16]. It should be noted that numerous functional ketones (keto-esters, keto-acetals, w-chloro-ketones) were converted into the corresponding functional alcohols very efficiently (Schemes 13.13 and 13.15). 

Aldols from a-haloketones. The Reformatsky-type reaction is readily effected at room temperature with the assistance of titanocene chloride, which is generated from Cp2TiCl2 and manganese in THF. Aromatic aldehydes are not suitable for the reaction as they tend to undergo pinacol coupling under the reaction conditions. 

Sequential cross-coupling reactions of 2,4-dichloropurine 69 have been conducted. 2,6-Disubstituted purine 69 was cross-coupled with MeZnBr to give monosubstituted purine 70, which underwent Suzuki cross-coupling with phenylboronic acid to furnish disubstituted purine 71. Recently, the synthesis of 6-(2-hydroxyethyl)purines was developed based on the Negishi palladium-catalyzed cross-coupling reactions of 6-chloropurines with the Reformatsky reagent followed by reduction by sodium borohydride and treatment with manganese(IV) oxide. ... 

Manganese-Mediated Barbier-and Reformatsky-like Reactions... 

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