Ethynyl magnesium bromide

The alcohol 172 obtained by reaction of 86 with ethynyl magnesium bromide on oxidation with manganese dioxide gave the ketone 17361 Glaser coupling of the ketone 173 gave an equimolar mixture of the two acyclic diketones 170 and 174. 

Adition of Grignard reagents. Reaction of 2,3-O-isopropylidene-D-ribose (62) with ethynyl magnesium bromide gives l,2-dideoxy-4,5-0-iso-propylidene-D-a//o-hept-l-ynitol (63), which is then converted into its 7-O-trityl ether (64). Treatment of 64 with TsCl/pyridine provides 2,3-0-isopropylidene-5-0-trityl-a-D-ribofuranosylethyne (65) which upon deprotection affords derivative 66 (Scheme 22).89... 

Ionone can be isolated from natural sources or synthesized in the laboratory. It is reacted with ethynyl magnesium bromide, or some other source of the anion derived from ethyne. to produce an alcohol (see Section 18.6). 

The monoterpenes 5(-i-)-carvone (10 Scheme 2, Nicolaou et al.) and / (—)-a-phellandrene (20 Scheme 3, Danishefsky et al.) are chosen as the starting materials for the syntheses of the diterpenoid skeleton of eleutherobin (1). Again, both routes require the separation of diastereo-mers by chromatography. The addition of 1-ethoxyvinyllithium to the TBS-protected aldehyde 13 (Scheme 2) leads to a mixture of diastereomeric alcohols (5 4 ratio in favor of the desired configuration at C8), which is separated by Nicolaou et al. after the alkynylation with ethynyl magnesium bromide in a later step. 13 was synthesized in close analogy to Trost et al. with bond formation between C9 and CIO via Claisen rearrangement (Scheme 2) [17]. 

Aryl tellurium halides react with aliphatic and aromatic Grignard reagents, with ethenyl magnesium halides , with ethynyl magnesium bromide with dimethyl and diethyl cadmium , with 2-(diphenylphosphino)-phenyl lithium, and with phenyl mercury chloride to produce aryl organo telluriums (p. 416). 

There are numerous applications of acetylides in the preparation of a-hydroxyalkynes, the following being illustrative of the general procedures. For the preparation of ethynyl-p-ionol (2), a key carotenoid building block, P-ionone (i) is condensed with ethynyl magnesium bromide (4) in ether [2], or with lithium acetylide (5) in liquid ammonia [7], in 87% and 75% yields, respectively (Scheme 1). The lower yield obtained with lithium acetylide probably reflects the propensity of P-ionone (3) to enolize under the reaction conditions. 

Details of the synthesis and reactions of glycofuranosylethynes, prepared via the reaction of 2,3 5,6-di-0-isopropylidene-a-D-mannofuranose with ethynyl magnesium bromide, have been published (see Vol. 8, p. 27). It is noteworthy that the glycofuranosylethynes do not obey Hudson s rules of isorotation. 

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