Organomanganese reagents 1,4-addition

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... 

Good yields of 1,4-addition products have also been obtained with alkylidene malonate esters which generally react with organomanganese reagents in the absence of copper salts9 (see Table IV). 

Scheme 2.S7. Copper-catalyzed Michael addition reactions between organomanganese reagents and pulegone.

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]. 

Benzylic organomanganese reagents prepared by direct insertion of activated manganese metal display the same behavior (Scheme 2.60) [131]. Excellent results are also obtained for 1,4-additions of organomanganese reagents to unsaturated esters in the presence of CuCI (3 mol%) [127]. 

The organomanganese reagents are comparable to ceriummagnesium ate complexes in almost complete addition to aldehydes in the presence of ketones. 

Overall, the isolated yields obtained from using benzyl sulfonates and phosphates were lower than those from using benzyl halides. However, this unusual oxidative addition to the C—O bond of benzyl sulfonates and phosphates under mild conditions and the resulting organomanganese reagents provide a new... 

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). 

Moreover, the reaction of /3-alkoxyalkylidenemalonic esters with organomagne-sium compounds leads to the dialkylated product (addition-elimination-addition), whatever the stoichiometry of the reactants (Scheme 13.34). With organomanganese reagents such a drawback is never observed and it is possible to prepare at 0 C the monoaddition product. It is also possible to obtain the addition-elimination product after acidic hydrolysis. 

It should be emphasized that with less reactive Michael acceptors such as enones, organomanganese reagents generally lead to a mixture of 1,4-addition product and reductive /3-dimerization products. In addition, the formation of the 1,2 addition product is sometimes also observed. The 1,4 addition product is only exceptionally obtained as a main product. 

The Cu-catalyzed conjugate addition of organomanganese reagents to a,/3-ethyle-nic aldehydes gives similar results than those obtained via lithium organocuprates in the presence of trimethylchlorosilane (Scheme 13.41) [36]. However, the reaction is easier to carry out since the aldehyde is obtained in one step instead of the two steps required with an organocuprate. It is important since the partial aldoli-... 

---