Acetylenic Grignard reagents, reactions with

Acetylenic Grignard reagents react with carbon dioxide (CO2) to yield carboxylic acids of the type RC CCOOH. The reactions with ethylcarbonate [CO(OEt)2] or ethylchloro-... 

Acetylene Grignard reagents, which are useful for further synthesis, are formed by the reaction of acetylene with an alkyhnagnesium bromide. 

Chloroacetaldehyde was prepared by heating its crystalline polymer and collecting the distillate in ether. The ethereal solution was at once reacted with the acetylenic Grignard reagent according to the procedure described above. After removal of the ether, the reaction mixture was concentrated as far as possible with a water pump. The residue at this point contained tneso-divinylacetylene dichlorohydrin, CHaCl—CHOH—C=C—CHOH—CHjCl, and probably the d,l isomer. When distillation was attempted by heating the reaction mixture strongly, it decomposed in an explosive manner. 

In 1999, Sekiguchi et al. prepared the first silyl acetylene dendrimers 255 and 256 with up to 22 Si atoms and 21 acetylene units (Schemes 35 and 36).358 The preparation of 255 and 256 has been achieved by the reaction of the triple Grignard reagent 257 with the trisila diyne 258 and the heptasila hexayne 259, respectively. 

Coupling reactions between allylic halides and alkynylcoppers have been rather heavily investigated as routes to stereochemically defined polyenyl natural products. The CuCl-catalyzed reaction of acetylenic Grignard reagents with chlorine substituted allylic chlorides has been employed in the synthesis of stereochemically pure 1,3,5-undecatrienes... 

Acetylenic Grignard reagents are commonly prepared by reaction of the appropriate 1-alkyne with an alkyl Grignard reagent, such as ethylmagnesium bromide. 

Anhydrous tetrahydrofuran from Matheson, Coleman and Bell Chemical Company was used for the reactions. Freshly opened bottles gave no effervescence when mixed with powdered calcium hydride. If smaller amounts of tetrahydrofuran are used, the acetylenic Grignard reagent often crystallizes out of the reaction mixture. 

Acetylenic carbinols are prepared by the interaction of sodium acety-lides or acetylenic Grignard reagents with aldehydes. The formation and reaction of the metallic acetylide may be combined into a single operation. For example, an alkylacetylene in ether solution is treated successively with ethylmagnesium bromide and formaldehyde to give the acetylenic alcohol such as 2-heptyn-l-ol (82%). ... 

In fact, the solubility of certain acetylenic Grignard reagents in diethyl ether is low and, in some instances, oily matter separates from solution. In this case, diethyl ether may be replaced by another solvent with higher solubility, but oily or slurry-like Grignard reagents have little effect on the reaction processes. Tetrahydrofuran shows excellent solubility properties and is used extensively for the preparation of acetylenic Grignard reagents. 

Some examples of the lower reactivity of acetylenic Grignard reagents are the 1,2-addition reactions involving benzonitrile [29], and nucleophilic substitution reactions with halogen compounds that are limited to those highly reactive compounds, such as... 

Acetylenic Grignard reagents are effective for reaction with conjugated compounds such as -ionone, which is an important starting material for the preparation of carotenoids that readily undergoes enolation under basic conditions. Some examples of synthetic processes are given [Eqs. (30-33) 46-49]. 

Acetylenic ketones can be prepared in moderate yield by the reaction of acetylenic Grignard reagents with acid chlorides or anhydrides [Eq. (41) 75-78]. Alkynyl magnesium chloride reacts with acetic anhydride to give acetylenic ketones in good yield (see Table 4, entry 17). 

THF is useful in the malonic ester synthesis since it dissolves many sodio derivatives. Use of aqueous THF facilitates diazotization of salts of aminopolyphenyls which are sparingly soluble in water and is recommended also for the Schiemann reaction. It is superior to ether as solvent for coupling of an acetylenic Grignard reagent with a propargylic halide. Cremlyn and Chisholm found THF superior to dioxane or Cellosolve as solvent for the hydrogenation of cholesterol at ordinary temperature and pressure with perchloric acid as catalyst. 

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