Trimethylsilylpropynoic acid reacts with thionyl chloride to give a mixture of trimethylsilylpropynoyl chloride and 3-chloro-3-trimethylsilyl-2-propenoyl chloride whose ratio depends on the reaction conditions (temperature, reactant ratio). Dimethylformamide almost does not catalyze the reaction. Treatment of trimethylsilylpropynoic acid with oxalyl chloride in the presence of 0.04 equiv of DMF at room temperature ensures selective formation of trimethylsilylpropynoyl chloride (yield 80%).

A highly efficient one-pot procedure was developed for the synthesis of 3-trimethylsilylpropynamides by acylation of amines with trimethylsilylpropynoyl chloride generated in situ. Selective N-acylation and N,O-bis-acylation of β-amino alcohols with formation of, respectively, N-(hydroxyalkyl)propynamides and 2-methyl-2-[3-(trimethylsilyl)propynoylamino]propyl 3-(trimethylsilyl)propynoate were accomplished with high yields. 3-(Trimethylsilyl)propynoic acid amides are valuable intermediates in the synthesis of biologically important heterocyclic compounds, such as chiral 2-trimethylsilyldihydro-1,3-oxazoles [1], trimethylsilylidenehydantoins [2], 1,5-trisubstituted 1H-1,2,3-triazoles [3], indoloquinolines [key compounds in the total synthesis of alkaloids (±)-lysergic acid and (±)-LSD] [4], as well as in the regio-and stereocontrolled synthesis of 3-carbamoylcyclopentenones as chiral synthetic intermediates or ligands [5], tetra-(hexa)hydrofuro[3,4-e]isoindol-6-ones as intermediate products in the synthesis of antibiotic lactonamycin [6], and unsaturated γ-[7] and δ-lactams [8].

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A highly effective procedure has been developed for desilylation of 3-trimethylsilylprop-2-ynamides in the presence of KF-Al 2 O 3 as catalyst. The corresponding terminal prop-2-ynamides were obtained in high yield in methanol at 25°C using 5 mol % of the catalyst (reaction time 20 min). Rise in temperature leads to the formation of Z,E-3-methoxyprop-2-enamides or 3,3-dimethoxypropanamides as a result of tandem desilylation-addition of methanol, depending on the conditions. The synthetic strategy silylation-desilylation of triple bond is widely used in fine organic synthesis, in particular in total syntheses of highly efficient natural antibiotics [1]. This approach was partially reviewed in [2]. The presence of a trimethylsilyl group at triple C≡C bond stabilizes the latter so that it becomes inactive toward nucleophiles [3], organometallic compounds, and transition metal catalysts in various synthetic transformations [4]; as a result, regioselective cycloaddition of azides at the triple bond of various trimethylsilylalkynes becomes possible [5], the stability of compounds increases, and their solubility in organic solvents is improved.Desilylation of acetylenic compounds can be performed with the use of various reagents, among which such bases as alkali metal hydroxides [6], alkoxides [7], and carbonates [8] in protophylic solvents, as well as potassium [9] and ammonium fluorides [10] are used most frequently. We recently showed that successful desilylation may be achieved with the aid of even weak bases generated in protic medium from metal oxides (PbO 2 , MnO 2 , Co 2 O 3 , Ni 2 O 3 ) [11].Despite diversity of desilylating agents, published data on desilylation of silicon-containing acetylenic compounds with an activated triple bond are few in number. Desilylation of such compounds requires mild conditions, taking into account the possibility for undesirable addition of alcohol or water (used as solvent) at the terminal triple bond in the resulting alkynes by the action of base in protophilic medium.In the present work we developed an efficient procedure for desilylation of trimethylsilylacetylenes having an activated triple bond. 3-Trimethylsilylprop-2-ynamides Ia-Ig were selected as substrates, and KFAl 2 O 3 , as reagent. Solid-phase desilylation of trimethylsilylalkynes under microwave irradiation required excess KF-Al 2 O 3 (4 equiv) [12]. There are no published data on desilylation of trimethylsilylacetylene derivatives with an activated triple bond by the action of KF-Al 2 O 3 . O Ia-Ig KF-Al 2 O 3 (5 mol %) MeOH, 25°C, 20 min HC NR 1 R 2 O IIa-IIg R 1 = H, R 2 = H (a), Ph (b), PhCH 2 (c), 2,5-Cl 2 C 6 H 3 (d), 3-BrC 6 H 4 (e), HOCH 2 CMe 2 (f); R 1 R 2 N = morpholino (g).

Bei der Einwirkung von Diethylumin (II) auf den Trimethylsilyl‐propiolsäure‐ester (I) erfolgt Abspaltung der Trimethylsilylgruppe.