Acetylene Grignard reagent

Acetylenic Grignard reagents of the type RC CMgBr are prepared not from an acetylenic halide but by an acid-base reaction in which a Grignard reagent abstracts a proton from a terminal aUcyne... 

Sodium acetylide and acetylenic Grignard reagents react with aldehydes and ketones to give alcohols of the type... 

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

Jacobi reports using a variant of method A to access the A,B,E-ring system of wortmannin.14 The sequential addition of methyl lithium and acetylenic Grignard reagent followed by triflation proceeds from 7 to the corresponding triflate 8 in 74% yield (Fig. 4.13). Subsequent carbonylation of the alkyne and the phenol produces the acyl oxazole 9, which is smoothly converted into the furanolactone 10 over three more steps. 

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. 

Unlike perfluoroaliphatic organometallics, perfluoroolefimc and perfluoro-acetylenic Grignard reagents have a greater thermal stability and can be prepared and used as intermediates at temperatures around 0 °C [40]... 

Our first goal was to develop a scaleable route to the single enantiomer propargylic alcohol. The racemic alcohol was readily produced on a multi-kilogram scale by alkylation of the phenol with inexpensive bromoacetaldehyde diethyl acetal, hydrolysis to the aldehyde, and addition of the acetylenic Grignard reagent. With this material at hand we developed an efficient bioresolution process that esterified the alcohol in the presence of Chirazyme L9 (Scheme 30.7).26 At this point... 

Furthermore, such a C3 -> C4 ring expansion could even be induced by lithium chloride. Thus, the cyclopropylcarbinol 228, prepared by addition of acetylenic Grignard reagents to the cyclopropanecarboxaldehyde 171a in 80-90% yield1101, was transformed into the tosylate 229 upon successive treatment with one equivalent of methyllithium in ether at 0 °C and with one equivalent of tosyl chloride at —40 °C, lithium chloride being formed as by-product. The formation of tosylate 229 appeared, however, to be strongly dependent upon the nature of the solvent effectively, the same... 

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 Grignard reagents are less active than sodium alkydes but are readily alkylated by benzyl halides as well as by alkyl sulfates and sulfonates.. . The Grignard reagents are conveniently prepared from the acetylenes and ethylmagnesium bromide in ether solution. 

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%). ... 

Acetylenic tertiary alcohols are prepared from sodium acetylides or acetylenic Grignard reagents and ketones in the same manner as described for primary and secondary alcohols (method 88). Dimethylethynylcarbinol is prepared from acetone, aqueous potassium hydroxide, and acetylene in an autoclave at 100° and 300 p.s.i. Ketones ate sometimes treated with an acetylide prepared from acetylene and a solution of sodium or potassium alkoxide in /-amyl alcohol. " Another procedure utilizes... 

Olefinic acetylenes of the general formula RCH= =CHC CR are prepared by coupling the a,/S-dibromo ethers with an acetylenic Grignard reagent followed by elimination of halogen and alkoxyl groups. Over-all yields are approximately 60%. ... 

Isomerization of acetylenic Grignard reagents affords the corresponding cyclic alkenyl Grignards [2,7]. Many cyclizations of acetylenic Grignard reagents are found in the literature [9]. Equations (37) [118,119] and (38) [119] represent recent, synthetically useful examples, in which the silyl group plays a dual role to facilitate the cyclization and to increase the stereoselectivity. 

III. PREPARATION OF ACETYLENIC GRIGNARD REAGENTS A. Preparations and Properties... 

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