Trimethylsilyl-protected alkyne

A recent convenient method for the preparation of 1-bromoalkynes in excellent yields (>90%) consists in the treatment of terminal acetylenes with the triphenylphosphine/tetra-bromomethane bromination reagent [81], In a further new development, 1-bromo- and 1-iodoacetylenes 137 are obtained by reacting trimethylsilyl-protected alkynes 136 with either N-bromo- (NBS) or 7V-iodosuccinimide (NIS) in the presence of silver nitrate [82] [Eq. (23)]. 

Ethynyl-2-(ethynylphenyl)-4-nitroaniIine. See the general procedure for the deprotection of trimethylsilyl-protected alkynes. 74 (0.10 g, 0.27 mmol) was deprotected to the terminal alkyne and the free amine using the procedure described above using K2CO3 (0.19 g, 1.35 mmol), MeOH (15 mL), and CH2CI2 (15 mL). The reaction mixture was allowed to stir at room temperature for 2 h. The resultant mixture was subjected to an aqueous workup as described above. Due to the instability of conjugated terminal alkynes, the material was immediately used in the next step without additional purification or identification. 

Methyl 4-ethynyIbenzoate (89). See the general procedure for the deprotection of trimethylsilyl-protected alkynes. The compounds used were methyl 4-(trimethylsilylethynyl)benzoate (0.75 g, 3.23 mmol), K2CO3 (2.23 g, 16.15 mmol), MeOH (50 mL) and CH2CI2 (50 mL) for 2 h. Extraction of the product afforded 0.49 g of the desired product that was immediately reacted in the next step. 

General Procedure for the Deprotection of Trimethylsilyl-Protected Alkynes. To a round bottom flask equipped with a stir bar were added the protected alkyne, K2CO3 (5 equiv per protected alkyne), MeOH, and CH2CI2. The reaction was heated, and upon completion the reaction mixture was diluted with CH2CI2 and washed with brine (3x). The organic layer was dried over MgS04, and the solvent removed in vacuo. 

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