Grignard reagents, reaction-!-alkynes

Alkyl- and aryl-pyridazines can be prepared by cross-coupling reactions between chloropyridazines and Grignard reagents in the presence of nickel-phosphine complexes as catalysts. Dichloro[l,2-bis(diphenylphosphino)propane]nickel is used for alkylation and dichloro[l,2-bis(diphenylphosphino)ethane]nickel for arylation (78CPB2550). 3-Alkynyl-pyridazines and their A-oxides are prepared from 3-chloropyridazines and their A-oxides and alkynes using a Pd(PPh3)Cl2-Cu complex and triethylamine (78H(9)1397). 

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. 

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]. 

In the early 1980s, one of the first preparations of substituted allenes was reported, which employed a palladium-catalyzed cross-coupling reaction of allenyl halides [9]. In this study, allenyl bromides 13 and various Grignard reagents 14 were coupled in the presence of catalytic amounts of a Pd(0) species, generated in situ by reduction of a Pd(II) salt. Trisubstituted allenes 15 were obtained with high regioselectivity (allene 15 alkyne 16 = 90 10 to 99 1) (Scheme 14.5). 

Hydroxymethylated cyclopropenes, which can be readily prepared by Rh-catalyzed reaction of diazoesters and alkynes, are good snbstrates for nncatalyzed and Cu-catalyzed carbomagnesiation. For example, a range of substitnted cyclopropanes 82 can be synthesized in a regio- and stereoselective fashion by the Cu-catalyzed addition of Grignard reagents to (3-hydroxymethyl)cyclopropenes 81 (Scheme 57) . 

Besides electrophilic addition, terminal alkynes also perform acid-base type reaction due to acidic nature of the terminal hydrogen. The formation of acetylides and alkynides (alkynyl Grignard reagent and aUcylnyllithium) are important reactions of terminal alkynes (see Section 4.5.3). Acetylides and alkynides undergo nucleophilic addition with aldehydes and ketones to produce alcohols (see Section 5.3.2). 

Alternately, CpjZr can also be prepared by the reaction of Cp2ZrCl2with two equivalents of n-BuLi at —78°C E.-I Negishi, F. K. Cederbaum and T. Takahashi, Reaction of zirconocene dichloride with alkyl lithiums or alkyl Grignard reagents as a convenient method for generating a zirconocene equivalent and its use in zirconium promoted cyclization of alkenes, alkynes dienes, eneynes and diynes, Tetrahedron Lett. 27 2829 (1986). 

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