Grignard reagents with alkynes

An allylaluminum species, which was generated by the reaction of allyl Grignard reagent with diisobutylaluminum chloride, was found to react with terminal alkynes in... 

The CuBr-catalyzed reaction of a Grignard reagent with 1,2-allenyl ether in Et20 at 20 °C afforded terminal alkynes [53]. 

The alternative, reaction of a Grignard reagent with an alkynyl ketone, is not acceptable in this case. The acidic terminal alkyne C—H would transfer a proton to the Grignard reagent. 

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... 

Schiff bases also add Grignard reagents via a process utilizing only 50% of the available R groups easily (81), the process involving second-order kinetics and a four-center transition state. The reaction of Grignard reagents with weak acids, such as acetonitrile and alkynes has also been studied 84, 82). 

Ni-Catalyzed Reactions The nickel-catalyzed cross-coupling of alkenyl Grignard reagents with aryl nitrile derivatives has been exploited by Miller and coworkers [4]. The conditions are similar to those described in Scheme 22.2. In general, alkenyl Grignards were /Zmixtures and therefore provided styrene derivatives as a mixture of E and Z isomers in modest to good yields (43-80%). Milder conditions were later developed in the Ni-catalyzed arylcyanation of alkynes, in which the insertion of alkynes into an aromatic C-CN bond took place (Scheme 22.12a) [5, 21a, b]. The intramolecular version of the reaction was likewise reported, and cyclization in a 5-exo-dig fashion occurred (Scheme 22.12b) [21c]. The addition of Lewis acids, such as AlMe Cl, AlMe, and... 

Accordingly, iron-catalyzed coupling of tricyclo[4.1.0.0 ]hept-l-ylmagnesium bromide and related Grignard reagents with propargylic halides proceeds either in an overall Sn- or Sn fashion depending on the substitution pattern of the alkyne (Scheme 4-204). Terminal alkynes predominantly afford allenes via a Sn route, whereas trimethylsilyl-substituted alkynes lead to alkyne derivatives. ... 

Another feature of the Pd—C bonds is the excellent functional group tolerance. They are inert to many functional groups, except alkenes and alkynes and iodides and bromides attached to sp carbons, and not sensitive to H2O, ROH, and even RCO H. In this sense, they are very different from Grignard reagents, which react with carbonyl groups and are easily protonated. 

Addition of alkynes to a-alkoxy aldehydes is most favorably performed with the corresponding zinc reagents (Table 12)46. As with Grignard reagents, the chelation-controlled addition of zinc alkynes proceeds with higher diastereoselectivity when diethyl ether rather than tetrahydrofuran is used as reaction solvent. 

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