Organocopper allylic substitution

To explain tlie stereodieniistiy of tlie allylic substitution reaction, a simple stereoelectronic model based on frontier molecular orbital considerations bas been proposed fl55. Fig. G.2). Organocopper reagents, unlike C-nudeopbiles, possess filled d-orbitals fd - configuration), wbidi can interact botli witli tlie 7t -fC=C) orbital at tlie y-carbon and to a minor extent witli tlie cr -fC X) orbital, as depicted... 

Scheme 6.30. Potential reaction products from allylic substitution with organocopper reagents (= Nu).

Tab. 6.6. Results of allylic substitution of styrene system 163 with organocopper reagents.

Tab. 6.7. Results of allylic organocopper reagents. substitution of y-silyl- substituted allyl ic carbamates 181 with ...

SN2 -selective reactions between primary allylic substrates and organocopper reagents result in the creation of new chirality in previously achiral molecules, and it is tempting to try to take advantage of this for the development of enantioselective allylic substitution reactions. 

Allylic substitutions with nonstabilized C-nucleophiles are an important domain of organocopper chemistry [51]. However, on close inspection of the literature, it becomes apparent that regioselectivity in favor of the branched allylic alkylation products is only obtained with alkyl copper compounds, while aryl copper compounds mainly give the linear alkylation products. This observation was an incentive for Alexakis et al. [52] to probe the reactions of aryl zinc hahdes in the Ir-catalyzed allylic substitution (Scheme 9.18). 

Allylic halides usually give both SN2 products and products of substitution with an allylic shift (SN2 products) although the mixed organocopper reagent RCu— BF3 is reported to give mainly the SN2 product.22 Allylic acetates undergo displacement with an allylic shift (SN2 mechanism).23 The allylic substitution process may involve initial... 

When looking for a process to remove the reagent-directing o-DPPB group with concomitant formation of a new carbon skeleton bond, allylic substitution with organocopper reagents appeared to be a synthetically appealing candidate. 

Breit, B. Demel, P. Copper-mediated Diastereoselective Conjugate Addition and Allylic Substitution Reactions. In Modem Organocopper Chemistry, Krause, N., Ed. Wiley-VCH Weinheim, 2002 pp 188-223. 

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