Organocoppers reactions with

This procedure illustrates a general method for the preparation of alkenes from the pal 1 adium(Q)-cata1yzed reaction of vinyl halides with organo-lithium compounds, which can be prepared by various methods, including direct regioselective lithiation of hydrocarbons. The method is simple and has been used to prepare a variety of alkenes stereoselectively. Similar stoichiometric organocopper reactions sometimes proceed in a nonstereoselective... 

Scheme 2.30 Ring-opening reaction with organocopper reagents to form (E)-allyl 111 amines.

Scheme 2.31 Stereochemical course of ring-opening reactions with organocopper reagents.

Chiral (-E)-vinyl-substituted sulfoximines, in which the iV-substituent was derived from (+)-norephedrine or ( —)-(S)-l-phenylethylamine2, underwent addition reactions with organolithi-um and organocopper reagents1,2. The diastereoselection ranged from moderate to good. 

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. 

Buynak et al. reported the synthesis of representative 7-vinylidenecephalosporine derivatives bearing an axial allene chirality (Scheme 4.5) [9]. A chiral allene 24 was prepared stereoselectively utilizing the reaction of an organocopper reagent with propargyl triflate 23, obtained by a diastereoselective ethynylation of the ketone 22 with ethynylmagnesium bromide. Terminally unsubstituted allene 26 was synthesized via bromination of the triflate 23 followed by reduction of the bromide 25 with a zinc-copper couple. 

In this chapter, we will emphasize these recent developments, especially those that allow the preparation of organocopper species not accessible through the standard procedures involving organolithiums as precursors and their use in reactions with organic electrophiles. 

Hydrolysis of the enol ethers obtained from the substitution reaction with the organocopper reagent yielded chiral b-substituted aldehydes with ees of 62 and 73% for the Sn2" and Sn2 products, respectively. 

Sn2 Reactions with epoxides and aziridines are also synthetically useful. An example of epoxide cleavage with an organocopper reagent with sp carbon moieties is the enantioselective synthesis of (3S, 4S)-4-methyl-3-heptanol (53), an elm bark beetle (Scolytus multistriatus) pheromone [42]. The chiral epoxy oxazolidine 51 [43], prepared from (R)-phenylglycinol, reacted with a propylmagnesium bromide-derived cuprate at —70 °C to afford the oxazolidine 52 in 74% yield (Scheme 9.12). Compound 52 was converted into the target molecular 53 by conventional procedures. 

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