Organomanganese reagents chemoselectivity

Organomanganese reagents have also been used to prepare numerous simple or functionalized ketones in high yields.10 They can be also used to carry out in high yields, at room temperature, various chemoselective 1,2-addition reactions, for example to keto aldehydes.11... 

Alkylation of organomanganese reagents with alkyl bromides can also be improved by addition of CuCI (3 mol%). The reactions proceed at room temperature and are complete within a few hours [123, 130], The opening of epoxides is also improved under these conditions. The reaction also features good chemoselectivity, tolerating the presence of sensitive functions such as ketones (Scheme 2.59) [130]. 

Compared to Grignard compounds, organomanganese reagents combine high reactivity and increased chemoselectivity. Schneider and co-workers reported... 

Of course, this route seems very attractive for the preparation of functionalized organomanganese reagents since it is thus possible to circumvent the limitations due to the use of organomagnesium or lithium compounds as an intermediate. However, until now, only a few examples have been described since the activated manganese is often too reactive to be sufficiently chemoselective. Nevertheless, the first alkylmanganese bromide bearing an ester group has been prepared by this route (Sciieme 13.4). 

Organomanganese reagents react with alkylidenemalonic esters or related compounds to give the conjugate addition products in good yields [33], They are very chemoselective, thus the conjugate addition product is exclusively obtained even in the presence of an ester or a ketone (Scheme 13.33). 

Recently, a new efScient substitution reaction of ortho-acylated aryl chlorides by organomanganese reagents has been reported [43]. Yields are generally excellent and the reaction readily takes place under very mild conditions with an excellent chemoselectivity (Scheme 13.60). Indeed, halogenoalkanes (Cl, Br, I), nitriles, esters and ketones are tolerated. 

---