Ethynyl

In the direct synthesis of aryl terminal alkynes via Pd-catalyzed cross-coupling of aryl halides with ethynylmetals, formation of diarylethynes is one of the potential side reactions. Indeed, the Kumada coupling of 2-iodo-5-methylthiophene (29) with ethynylmagnesium chloride gave the desired 2-ethynyl-5-methylthiophene (30) in only 35% yield, along with 24% of bis(5-methyl-2-thienyl)ethyne (31) [29], The high propensity for H-Mg exchange reaction to occur was blamed for the diarylethyne formation. 

In order to avoid tedious separation of the isomers and to increase the scale of the reaction, protected alkynes were used. 2-Ethynyl-5-trimethyl-silylthiophene was used. The irradiation of 5-iodothiophene-2-carbalde-hyde in the presence of this compound gave only the expected substitution... 

Dibromovinyl)- (158) gave 2-ethynyl-5-isopropyl-3,6-dimethoxy-2-methyl-2,5-dihydropyrazine (159) (BuLi, THF—C6H14, -78°C, 90 min 83% mechanism ).528... 

R,3R,4R,5R)-2-ethynyl-5-methyltetrahydrofuran-3,4-diol (2S,3R,4R,5R)-2-ethynyl-5-methyltetrahydrofuran-3,4-diol (5-Deoxy-a-D-xylofuranosyl)ethyne (5-Deoxy-p-D-xylofuranosyl)ethyne... 

Several substituted 2-ethynylbenzaldehydes were then apphed to this copper-catalyzed four-component synthesis of 3,4-dihydro-2ff-pyrimido[2,l-fl]isoquino-Une under optimized conditions (Table 1, entry 10). The results are summarized in Table 2. The substitution by a fluorine atom at the para-position to the formyl group shghtly decreased the yield of 12b (55%, entry 1). The reaction with 2-ethynylbenzaldehydes Ic and Id containing a fluorine atom at the meta-position or methyl group at the para-position to the formyl group showed a good conversion to yield the desired tricyclic compounds 12c and 12d (74 and 71%, respectively, entries 2, 3). The use of 2-ethynyl-5-methoxybenzaldehyde le also gave tricyclic compound 12e (55%, entry 4). Overall, this four-component construction of 3,... 

S)-terf-Butyl 3-(2-(2-Ethynyl-5-oxopyrrolidin-l-yl)ethyl)-lff-lndole-l-car-boxylate (III-28)... 

Ethynyl-5-(ethynylphenyl)aniline. See the general procedure for the deprotection of trimethylsilyl-protected alkynes. The compounds used were 3-ethynylphenyl-6-(trimethylsilylethynyl)aniline (0.22 g, 0.75 mmol) K2CO3 (0.52 g, 3.75 mmol), MeOH (15 mL), and CH2CI2 (15 mL) for 2 h. Due to the instability of conjugated terminal alkynes, the material was immediately used in the next step without additional purification or identification. 

Cycloadditions of 1,6-diynes with 2-ethynyl-5,5-dimethyl-1,3,2-dioxaborinane (62) were also catalyzed by 6 to furnish stable arylboronates in good yields (Scheme 3.11) [48]. For example, a malonate-derived diyne underwent cycloaddition with 62 in the presence of 5 mol % of 6 at room temperature to afford the cycloadduct desired in 86% yield. However, the corresponding unsymmefrical diyne with one terminal methyl substituent required an increased catalyst loading of 10 mol %. Accordingly, regioisomers 63 and 64 were formed with a moderate selectivity at a 63/64 ratio of 1 2.4. 

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