Alkylation of acetylenes

PREPARATION OF ALKYNES BY ALKYLATION OF ACETYLENE AND TERMINAL ALKYNES... 

Preparation of Alkynes by Alkylation of Acetylene and Terminal Alkynes... 

Reactions that attach alkyl groups to molecular fragments are called alkylation reactions One way m which alkynes are prepared is by alkylation of acetylene... 

Alkylation of acetylene involves a sequence of two separate operations In the first one acetylene is converted to its conjugate base by treatment with sodium amide... 

Both CH3CH2CH2C=CH and CH3CH2C=CCH3 can be prepared by alkylation of acety lene The alkyne (CH3)2CHC=CH cannot be prepared by alkylation of acetylene because the required alkyl halide (CH3)2CHBr is secondary and will react with the strongly basic acetylide ion by elimination... 

Alkylation of acetylene and terminal alkynes (Section 9.6) The acidity of acetylene and terminal alkynes permits them to be converted to their conjugate bases on treatment with sodium amide. These anions are good nucleophiles and react with methyl and primary alkyl halides to form carbon-carbon bonds. Secondary and tertiary alkyl halides cannot be used, because they yield only elimination products under these conditions. 

Alkylation of acetylene to (3) goes in high yield, the cuprous derivative (4) is a stable solid, and the required reagent(s) cleanly transfers R to an enone. Problem Suggest a synthesis for the sedative laeparfynol (6). 

Sommelet, 30, 67 Alizarin indicator, 37, 33 Alkylation, of acetylene, 30, 15 of aniline with triphenylcarbinol, 30, 5 of e-caprolactam with dimethyl sulfate,... 

SAMPLE SOLUTION (a) An examination of the structural formula of 1-heptyne reveals it to have a pentyl group attached to an acetylene unit. Alkylation of acetylene, by way of its anion, with a pentyl halide is a suitable synthetic route to 1-heptyne. 

A third isomer, 3-methyl-1-butyne, cannot be prepared by alkylation of acetylene, because it requires a secondary alkyl halide as the alkylating agent. The reaction that takes place is elimination, not substitution. 

Alternatively, two successive alkylations of acetylene with CH3CH2CH2Br could be carried out to give 4-octyne (CH3CH2CH2C=CCH2CH2CH3), which could then be hydrogenated to octane. 

The necessary alkyne 9-tricosyne can be prepared by a double alkylation of acetylene. 

The alkynide anion is derived from 1-butyne by alkylation of acetylene. This analysis suggests the following synthetic sequence ... 

N-Alkylation—Secondary Mannich bases can give the corresponding tertiary derivatives by treatment with particular alkylation agents, such as epoxides (affording P-ami-noalcohols) and acrylic derivatives. Tertiary Mannich bases, mostly, are submitted to N-alkylation in order to produce stable quaternary ammonium salts to be subsequently subjected to deamination (Sec. A.2). However, different quaternary ammonium byproducts can be readily given by the reaction. " For instance, a base-catalyzed rearrangement is afforded by allyl ammonium salts 365 (Fig. 144), obtained by N-alkylation of acetylenic Mannich bases with ally] halides. " In the presence of sodium hydride, the compounds 365 yield a wide range of 3-amino-5-hexen-l-yne derivatives 366. 

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