Copper-catalyzed allylation

It may be concluded from die different examples sliown here tiiat die enantio-selective copper-catalyzed allylic substitution reaction needs ftirdier improvemetiL High enantioselectivities can be obtained if diirality is present in tiie leaving group of die substrate, but widi external diiral ligands, enantioselectivities in excess of 9096 ee have only been obtained in one system, limited to die introduction of die sterically hindered neopeatyl group. 

In copper-catalyzed Grignard reactions of allylic carboxylates, high y regioselectivity is observed when copper(I) cyanide is used as catalyst16. 

Table 12.1. Enantioselective Copper-Catalyzed Allylic Oxidation of Cyclohexene...

The method was later extended to the synthesis of a number of meroter-penoids from epoxygeranyl carbonates or acetates in a two-step approach combining titanocene catalysis with Stifle reactions (carbonates) [108,109] or copper-catalyzed allylic substitutions (acetates) [110-112], The cyclizations... 

Interaction of an electrophilic carbene or carbenoid with R—S—R compounds often results in the formation of sulfonium ylides. If the carbene substituents are suited to effectively stabilize a negative charge, these ylides are likely to be isolable otherwiese, their intermediary occurence may become evident from products of further transformation. Ando 152 b) has given an informative review on sulfonium ylide chemistry, including their formation by photochemical or copper-catalyzed decomposition of diazocarbonyl compounds. More recent examples, including the generation and reactions of ylides obtained by metal-catalyzed decomposition of diazo compounds in the presence of thiophenes (Sect. 4.2), allyl sulfides and allyl dithioketals (Sect. 2.3.4) have already been presented. 

Copper-catalyzed Asymmetric Allylic Alkylations with Alkylzinc Reagents 403... 

Hoveyda and co-workers also tested optically active A-heterocyclic carbenes and their silver complexes in copper-catalyzed reactions of allylic phosphates with dialkylzincs.402 The ratios of Sn2 SN2 products were higher than 98 2 and the ee varied from 34% to 98%. 

Scheme 6.97 Copper-catalyzed asymmetric allylic oxidation of bridged bicyclic alkenes.

Scheme 8. General mechanism of the copper-catalyzed allylic oxidation of alkenes (Kharasch-Sosnovsky reaction).

Scheme 10. Results of proline-copper catalyzed allylic oxidation, prom (105).] X-ray crystal structure of (R.Sf-complex 146. [Adapted from (106).]...

Scheme 6.42. Copper-catalyzed allylic substitution of mesylate 197 with an organozinc reagent.

In the 1952 paper mentioned above [3], Gilman reported on the formation of lithium dimethylcuprate from polymeric methylcopper and methyllithium. These so-called Gilman cuprates were later used for substitution reactions on both saturated [6] and unsaturated [7, 8, 9] substrates. The first example of a cuprate substitution on an allylic acetate (allylic ester) was reported in 1969 [8], while Schlosser reported the corresponding copper-catalyzed reaction between an allylic acetate and a Grignard reagent (Eq. 2) a few years later [10]. 

The moderate ees obtained with the copper arenethiolate ligands discussed above prompted a search for new chiral ligands for use in asymmetric allylic substitution reactions. The binaphthol-derived phosphoramidite ligand 32, used successfully by Feringa et al. in copper-catalyzed 1,4-addition reactions [37], was accordingly tested in the reaction between 21 and n-BuMgl. 

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