Organocopper reagents stoichiometric

One of the most popular methods for the synthesis of allenes is the Sn2 reaction of propargylic derivatives with organocopper reagents [1, 2], Most probably a study published in 1968-69 by Rona and Crabbe represents the first example of the Cu(I)-mediated SN2 reaction of propargylic electrophiles giving allenic products (Scheme 3.32) [69, 70], Since then, many researchers have used modified organocopper reagents with stoichiometric or catalytic amounts of Cu(I) salt. 

Copper-mediated or copper-catalyzed substitution reactions can be performed on a number of different substrates (Scheme 8.1). Stoichiometric organocopper reagents... 

The main disadvantage of this reaction is that it is necessary to use stoichiometric amounts, or more, of the organocopper reagent, together with stoichiometric amounts of the chiral auxiliary. The leaving group chiral auxiliary, however, can be recovered and recycled after the reaction. 

Many of the copper-mediated transformations summarized in the previous sections of this chapter can also be performed efficiently with catalytic amounts of copper salts or reagents. Indeed, some of the copper-catalyzed reactions have been discovered before the development of stoichiometric organocopper reagents. The focus of the last decade has been put on new copper-catalyzed transformations (e.g., conjugate reductions) and in particular on the discovery of chiral copper catalysts for highly enantioselective 1,4-addition and S -substitution reactions of prochiral substrates. 

Copper(i) catalysis of the addition of organomagnesium compounds to alkynes has been observed, but stoichiometric organocopper reagents, derived from organomagnesium compounds, are more effective in the absence of other activating features [4],... 

For reactions involving stoichiometric conversion of organomagnesium compounds into organocopper reagents, see Chapter 16. 

Mechanistic aspects of copper-catalyzed Grignard addition to a,/ -unsaturated carbonyl compounds have not attracted much attention, probably because of the complex nature of the reagent system [11], but it would resemble that of the 1,4-addition of stoichiometric or higher-order organocopper reagents that have been investigated extensively [15,18,223]. 

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