Grignard reagents, reaction with alkynes

Vinylic ethers. Vermeer et al. have extended the conversion of methoxyallene to 1-alkynes by reaction with Grignard reagents catalyzed by copper(I) halides (6, 146) to a synthesis of vinylic ethers, formulated in equation (11). The ethers... 

The acidic hydrogen present in terminal alkynes can undergo reactions with Grignard reagents. A sample reaction is shown. 

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. 

The coupling reaction of tellurides with Grignard reagents promoted by Ni(ll) was described many years ago by LJemura.143 Recently, bis-vinylic tellurides were reacted with alkynes in the presence of catalytic amounts of Ni(dppe)Cl2 and Cul leading to enynes with retention of the (Z)-stereochemistry (Scheme 128).306... 

Pasto [29] undertook a detailed study of the reaction of terminal propargyl chlorides 40 with Grignard reagents, and found an allene carbene-zwitterion intermediate 41 that could best rationalize the formation of the two alkynes 42 and 44 and allene 43 observed [Eq. (14)], the 8 2 mechanism discarded, or at least being the minor process involved in such a reaction. 

One convenient method for the preparation of alkene (11-14) and alkyne (15-16) derivatives of transition metals (Ni(II), Pd(II), Pt(II)) is the interaction of the corresponding metal halides with Grignard reagents [15-17] through a series of simple consecutive reactions(Eqs. 4-2, 4-3). The MCMs obtained are stable enough to be characterized in detail (Table 4-1). 

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). 

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