Alkynyl Grignard reagents salts

The action of alkynyl Grignard reagents on the pyridinium salt 67 affords solely 1,2-dihydropyridine derivative 68, whereas alkyl Grignard reagents yield mixtures of 1,2- and 1,4-dihydropyridines (equation 10). The contrasting behaviour of the two nucleophiles was explained by means of the Principle of Hard and Soft Acids and Bases". Application of the reaction to the action of the acetylenic Grignard compound 69 on l-methoxycarbonyl-2-methylpyridinium chloride gave the dihydropyridine derivative 70, which was transformed into ( ) -monomorine 71, a train pheromone of the pharao ant. ... 

The addition of Grignard reagents or organolithiums (alkenyl, alkyl, alkynyl, allyl or aryl) to nitroenamines (281)213 was reported by Severin to afford P-substituted-a-nitroalkenes.214 b Similarly, ketone enolates (sodium or potassium), ester enolates (lithium) and lactone enolates (lithium) react to afford acr-nitroethylidene salts (294) which, on hydrolysis with either silica gel or dilute acid, afford 7-keto-a,(3-unsaturated esters or ketones (295)2l4c-d or acylidene lactones (296).214 Alternatively, the salts (294, X s CH2) can be converted to -y-ketoketones (297) with ascorbic acid and copper catalyst. 

A-Acylpyridinium salts are more reactive than the A-alkyl derivatives and afford more stable dihydropyridine products on addition of nucleophiles. Organocuprates are utilized for entry into 2-alkynyl-substituted quinoline systems (Equation 53) <2005TL8905>. They have the advantage of superior selectivity over Grignard reagents, which yield a mixture of the 2- and 4-substituted products. The reaction has been expanded to include isoquinolines and pyridines. 

The reaction of sulfinates with alkynyl iodonium salts was successful, as these substrates are less easy to oxidize. Nevertheless, Waser and Chen demonstrated that EBX reagents can also be useful to synthesize alkynyl sulfones, as they allow a new one-pot procedure starting directly from Grignard reagents (Scheme 36) [161]. In this protocol, DABSO (DABCO-S02) is added after formation of the Grignard reagent. Addition of DME and TIPS-EBX 52 gives aryl alkynyl sulfones in 46-85% yield. Eor base sensitive substrates, it was also possible to start from aryl iodides and use a palladium catalyst. 

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