Normant reagents, addition alkynes

The fruitfulness of the idea of a stepwise addition with an independent variation of the addends was brilliantly illustrated by Normant s studies, which resulted in the elaboration of a general method of alkene synthesis based on the reaction of alkyne carbometallation. Basically this reaction represents a case of the well-known nucleophilic addition to a carbon-carbon triple bond. In the Normant reaction, however, the initial addition of a nucleophile (an organome-tallic reagent) across the triple bond results in the formation of a stabilized carbanion-like intermediate equivalent to a vinyl carbanion. This intermediate can similarly be further reacted with an external electrophile. Most typically, copper-modified Mg or Li reagents, which are unable to react with acidic acetylenic hydrogens, are used in this sequence. 

Alkenes. Normant et al. have developed a method for a regiospecific synthesis of 1-alkenes by addition of organocopper reagents to 1-alkynes. The copper reagents are prepared by the reaction of a Grignard reagent with cuprous bromide in ether at -40. The 1-alkyne is then added to this solution to form a... 

Knochel and Normant have demonstrated that functionalised allylzinc reagents undergo a regiospecific addition to terminal alkynes to give 1,4-dienes (126) in moderate to good yield (Scheme... 

Additions of organometallic reagents to 1-alkynes continue to play a prominent role in the regio- and stereo-selective synthesis of olefins. A convenient procedure for the stereospecific synthesis of trisubstituted olefins, based on Normant s work on the addition of alkyl copper(l) complexes to 1-alkynes, is outlined in Scheme 10. The use of House s dimethyl sulphide-copper(i) bromide complex minimizes... 

Normant and coworkers have described the syn-addition of alkylcopper compounds to various functionalized alkynes. The regioselectivity is explained by com-plexation of the alkenylcopper reagent formed in the addition reaction. Using this methodology, various homoallylic alcohols can be obtained. This methodology was applied to the synthesis of myrcenol 73 (Scheme 9.22) [33]. 

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