L- -3-butyn

A mixture of 0.10 mol of freshly distilled 3-methyl-3-chloro-l-butyne (see Chapter VIII-3, Exp. 5) and 170 ml of dry diethyl ether was cooled to -100°C and 0.10 mol of butyllithium in about 70 ml of hexane was added at this temperature in 10 min. Five minutes later 0.10 mol of dimethyl disulfide was introduced within 1 min with cooling betv/een -100 and -90°C. The cooling bath vjas subsequently removed and the temperature was allowed to rise. Above -25°C the clear light--brown solution became turbid and later a white precipitate was formed. When the temperature had reached lO C, the reaction mixture was hydrolyzed by addition of 200 ml of water. The organic layer and one ethereal extract were dried over potassium carbonate and subsequently concentrated in a water-pump vacuum (bath... 

In the flask were placed 40 ml of ethanol, 10 ml of water, 12 g of finely powdered CuCN and 0.40 mol of 3-bromo-l-butyne (compare VIII-2, Exp. 3). The mixture was warmed to 55°C and a solution of 26 g of KCN in 60 ml of water was added drop-wise or in small portions care was taken that complete dissolution of the copper cyanide did not occur (note 2). The temperature of the mixture was maintained close to 60°C throughout the period of addition. The conversion was terminated... 

In the receiver was collected almost pure 3-bromo-3-methyl-l-butyne, n 1.466B, in 50iS yield. The residue consisted of the HBr adduct of the acetylenic bromide. 

The labile hydroxyl group is easily replaced by treatment with thionyl chloride, phosphorous chlorides, or even aqueous hydrogen haUdes. At low temperatures aqueous hydrochloric (186) or hydrobromic (187) acids give good yields of 3-halo-3-methyl-l-butynes. At higher temperatures these rearrange, first to l-halo-3-methyl-1,2-butadienes, then to the corresponding 1,3-butadienes (188,189). 

Butyr aldehyde Butanal 116 C4H8O 3-Methyl-l-butyne 48 CsHs... 

A number of alternative multi-step procedures for the synthesis of a-tert-alkyl ketones are known, none of which possess wide generality. A previous synthesis of 2-tert-penty1cyclopentanone involved reaction of N-1-cyclopentenylpyrrol 1 dine with 3-chloro-3-methy1-l-butyne and reduction of the resulting acetylene (overall yield 46 ). However, all other enamines tested afford much lower yields. Cuprate addition to unsaturated ketones may be useful in certain cases. Other indirect methods have been briefly reviewed. ... 

Some studies seeking preferred conditions for this reaction have been reported. Optimum yields of 1-ethoxy-1-propyne and 1-ethoxy-l-butyne are found when the product is worked up before allowing the ammonia solvent to evaporate, as the product evidently volatilizes with the ammonia. An experiment with 1-ethoxy-1-propyne showed a marked increase in yield when ammonia predried over calcium hydride was used instead of ammonia directly from the cylinder. A twofold excess of ethyl bromide is required to obtain a good yield of l-ethoxy-l-but5me, since elimination apparently competes with alkylation in this case. 

Hexyne, 2-hexyne, 3-hexyne, 3-methyl-Hpentyne, 4-methyl-l-pentynep 4-methyl-2-pentyne, 3.3-dimethyl-l-butyne... 

R = Me, R = H) with cyclohexenol in the presence of F ion followed by NaOCl oxidation gave the tricyclic ether 61 in 65% yield (Scheme 9) [29]. The use of propargyl alcohol and propargyl thiol led, via the acetylenic oximes, to fused tetrahydrofuranoisoxazoles 62 a and 62 b, and tetrahydrothiopheno[3,4-c]isoxa-zole 62 c, respectively. Reaction of l-butyn-4-ol with 0-trimethylsilyl a-bro-moaldoxime 52e (R = R = Me) led to the tetrahydropyranoisoxazole 62 d. 

EtjNH reacts with acetylene in the presence of copper(I) chloride or acetylide to give 3-diethylamino-l-butyne (Scheme 4-10) [243-247]. 

Similar reactions with primary and secondary amines result in the formation of 3-aUcylamino- or 3-dialkylamino-l-butyne in 30-80% yield (TON = 3-9) [243-247]. In one example, the TOP could be estimated as 0.2 h" [246]. Enamines were proposed as reaction intermediates. It was later shown that enamines effectively react with terminal aUcynes, including acetylene, to afford the expected aminoalkynes without catalyst or, more rapidly, sometimes exothermically, in the presence of CujCf [248]. Aromatic amines do not react under the same conditions. However, in the presence of organic acids, e.g. acetic acid, 3-arylamino-l-butynes can be isolated in moderate yields (Eq. 4.59) [246, 247, 249]. 

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