Alkynyl Grignard reagents

In general, the reaction can be performed only with organometallics of active metals such as lithium, sodium, and potassium, but Grignard reagents abstract protons from a sufficiently acidic C—H bond, as in R—C=C—H —> R—C=C—MgX. This method is best for the preparation of alkynyl Grignard reagents. ... 

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). 

Crotylzinc bromide can also add twice to alkynyl Grignard reagents and the resulting bis-adducts exclusively incorporate two 2-butenyl groups (equation 141)169,170. 

In general, monoaddition was observed when a terminal alkyne was directly treated with an excess of the allenylzinc reagent itself. However, starting from an alkynyl Grignard reagent predominantly led to bis-addition compounds (equation 152)185. 

Alternatively, the reaction of cyclopropylethynylmagnesium bromide with cyclo-propanone hemiacetal gives l-(cyclopropylethynyl)cyclopropanol (equation 152)232. The reaction of cyclopropanone acetal with other alkynyl Grignard reagents serves as a general route to alkynylcyclopropanols. Similarly, alkynyllithium derivatives of vitamin D were coupled with cyclopropane carbonyl isoxazolidine to give the corresponding alkynyl-cyclopropyl ketones (equation 153). 

Alkynyl Grignard reagent 8 is directly applied in a THF solution for conversion of 10 into 11. 

A zinc alkoxide is formed in the first step. How will this complex react with alkynyl Grignard reagent 8 ... 

M. Umeno, A. Suzuki, Alkynyl Grignard Reagents and Their Uses, in Handbook of Grignard Reagents (G. S. Silverman, P. E. Rakita, Eds.), Marcel Dekker Inc., New York, 1996, 645-666. 

In the majority of cases, organolithium compounds and Grignard reagents contain polarized but covalent carbon—metal bonds. Lithioalkanes, -alkenes, and -aromatics, on the one hand, and alkyl, alkenyl, and aryl magnesium halides, on the other hand, are therefore formulated with a hyphen between the metal and the neighboring C atom. Only lithiated alkynes and alkynyl Grignard reagents are considered to be ionic—that is, species with carbon, metal bonds similar to those in LiCN or Mg(CN)2. 

Table 8.1 shows that the pXa of CH3-H is 60. Since CH4 is a very weak acid, CH3 is a very strong base. Alkyl Grignard reagents are similar in base strength to - CH3, but alkynyl Grignard reagents are somewhat weaker bases. Both reactions (a) and (b) occur as written. 

AminoqninoliHes. Chloroformamidines (1) reacc with alkynyl Grignard reagents to afford the hitherto unknown propiolic acid amidincs (2), which can be cyclircd to 2-aminoquinolines (3) with PPA at temperatures of about 150°. 

Compounds containing four alkynyl groups attached to a single atom (C, Si, Ge) have been obtained by the coupling of alkynyl Grignard reagents with the appropriate tetrahalide . ... 

The Ni-catalyzed cross-coupling reaction of alkynyl Grignard reagents 60 with ( )- or (Z)-dichloroethene 61a,b has been applied to a simple procedure for the preparation of the protected fomi 62a,b of a highly unstable synthon, as hexa-3-ene-l,5-diyne [Eq. (23). Separation of the diastereomers 62a and 62b is facile since the former is an oil and the latter is a solid [35]. 

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