Alkylation, trimethylsilyl acetylene

Reactions of salts of 1,2,3-triazole with electrophiles provide an easy access to 1,2,3-triazol-jV-yl derivatives although, usually mixtures of N-l and N-2 substituted triazoles are obtained that have to be separated (see Section 5.01.5). Another simple method for synthesis of such derivatives is addition of 1,2,3-triazole to carbon-carbon multiple bonds (Section 5.01.5). N-l Substituted 1,2,3-triazoles can be selectively prepared by 1,3-dipolar cycloaddition of acetylene or (trimethylsilyl)acetylene to alkyl or aryl azides (Section 5.01.9). 

Additionally, acetylene itself is a useful two-carbon building block but is not very convenient to handle as it is an explosive gas. Trimethylsilyl acetylene is a distillable liquid that is a convenient substitute for acetylene in reactions involving the lithium derivative as it has only one acidic proton. The synthesis of this alkynyl ketone is an example. Deprotonation with butyl lithium provides the alkynyl lithium that reacted with the alkyl chloride in the presence of iodide as nucleophilic catalyst (see Chapter 17). Removal of the trimethylsilyl group with potassium carbonate in methanol allowed further reaction on the other end of the alkyne. 

The hydroboration with 1 1 stoichiometry reduces the percentage of monohydroboration, drastically. However, for comparison the hydroboration of alkynes with 1 1 alkyne-9-BBN under essentially neat condition provides better line shapes for the carbon a to boron and no interference from solvent absorptions. (Trimethylsilyl)acetylene (le) results in only P-mono- (P to TMS) and dihy-droboration products (Eq. 5.23), the behavior common to nonsilylated terminal acetylenes, but differing in the extent of mono- and dihydroboration. Moreover, it is found that this silylalkyne is less reactive toward 9-BBN as compared with its alkyl counterpart. In addition, the steric repulsions between the substituted boron atom, and the a-TMS groups are sufficiently large so as to prevent their site from competing with the alternative, unencumbered position. 

Oxidations. Aikynes of high nucleophilicity such as ethoxy-(trimethylsilyl)acetylene react with electrophilic O3 to give vicinal dicarbonyl derivatives. In contrast to alkylated or ary-lated acetylenes, neither products of complete C-C cleavage nor peroxidic materials were detected as primary products. Ethoxy-(trimethylsilyl)acetylene reacted with ozone to yield a mixture of ethyl 2-oxo-2-(trimethyl)acetate (13) and ethyl trimethylsUyl oxalate (14) (eq 11). The mechanism of this reaction was also discussed. ... 

Aiming to develop an efficient route to 1,2-dihydropyridines, Ogoshi et al. performed extensive mechanistic studies with a stoichiometric amount of nickel complex [16]. These studies revealed a plausible mechanistic pathway for this particular cycloaddition reaction. Further experimentation revealed that the use of electron-donating, sterically hindered phosphines actually renders the reaction catalytic. Three catalytic examples were reported. These include the cycloaddition of alkyl-aryl alkynes (72 and 73) and trimethylsilyl acetylene (74) (Scheme 2.19). The moderate yields of cycloadducts and small substrate scope still need to be addressed. 

Etherification. The reaction of alkyl haUdes with sugar polyols in the presence of aqueous alkaline reagents generally results in partial etherification. Thus, a tetraaHyl ether is formed on reaction of D-mannitol with aHyl bromide in the presence of 20% sodium hydroxide at 75°C (124). Treatment of this partial ether with metallic sodium to form an alcoholate, followed by reaction with additional aHyl bromide, leads to hexaaHyl D-mannitol (125). Complete methylation of D-mannitol occurs, however, by the action of dimethyl sulfate and sodium hydroxide (126). A mixture of tetra- and pentabutyloxymethyl ethers of D-mannitol results from the action of butyl chloromethyl ether (127). Completely substituted trimethylsilyl derivatives of polyols, distillable in vacuo, are prepared by interaction with trim ethyl chi oro s il an e in the presence of pyridine (128). Hexavinylmannitol is obtained from D-mannitol and acetylene at 25.31 MPa (250 atm) and 160°C (129). 

Me3SiI, CH2CI2, 25°, 15 min, 85-95% yield.Under these cleavage conditions i,3-dithiolanes, alkyl and trimethylsilyl enol ethers, and enol acetates are stable. 1,3-Dioxolanes give complex mixtures. Alcohols, epoxides, trityl, r-butyl, and benzyl ethers and esters are reactive. Most other ethers and esters, amines, amides, ketones, olefins, acetylenes, and halides are expected to be stable. 

These are good dienophiles. and aryl vinyl sulfones have found use as equivalents of ethylene and ketene through functional modifications of their adducts. However, as the base-induced elimination of a sulfinic acid to yield an olefin occurs only with difficulty, they are not direct precursors of acetylene equivalents, unless suitably modified as in ( )-l-phenyl-sulfonyl-2-trimethylsilyl ethylene (PhS02-CH=CH-TMS). In its cycloadducts the elimination to an alkene is smoothly realized by the fluoride ion. If an alkylation step is previously carried out on the adduct, the overall process realizes an indirect addition of a terminal acetylene, as in the examples given here [533]. 

Tetrafluoroammonium hexafluoromanganate, 4378 Tetrafluoroammonium hexafluoronickelate, 4379 Tetrafluoroammonium hexafluoroxenate, 4380 Tetranitromethane, 0543 Titanium tetraperchlorate, 4164 1,1,1 -Triacetoxy-1,2-benziodoxol-3-one, 3604 Trifluoromethyl hypofluorite, 0352 Trimethylsilyl chlorochromate, 1297 Trioxygen difluoride , 4317 Uranium hexafluoride, 4369 Vanadium trinitrate oxide, 4758 Vanadium(V) oxide, 4860 Vanadyl perchlorate, 4146 Xenon hexafluoride, 4371 Xenon tetrafluoride, 4347 Xenon tetrafluoride oxide, 4340 Xenon tetraoxide, 4857 Xenon trioxide, 4851 Xenon(II) pentafluoroorthoselenate, 4376 Xenon(II) pentafluoroorthotellurate, 4377 Zinc permanganate, 4705 ACETYLENIC PEROXIDES ACYL HYPOHALITES ALKYL HYDROPEROXIDES ALKYL TRIALKYLLEAD PEROXIDES AMINIUM IODATES AND PERIODATES AMMINECHROMIUM PEROXOCOMPLEXES BIS (FLUOROOXY)PERHALOALKANES BLEACHING POWDER CHLORITE SALTS... 

Silyl, germanyl and stannyl alk-l-ynyl ketones have been prepared from 2-lithio-2-(trimethylsilylethynyl)-l,3-dioxolane 448. The deprotonation of the dioxane 447 with n-BuLi at — 65 °C afforded the acyl anion 448 which, after reaction with trimethylsilyl, trimethylgermanyl and trimethylstannyl chloride, gave the expected derivatives (Scheme 117)658. Hydrolysis of these products with 0.01 M sulfuric acid at room temperature in aqueous acetone gave the corresponding acyl derivatives 449. On the other hand, the reaction of the intermediate 448 with alkyl halides allows the synthesis of acetylenic ketones659. 

Unlike hydrazoic acid, trimethylsilyl azide is thermally quite stable. Even at 200° it decomposes slowly and without explosive violence. Accordingly it is a very convenient and safe substitute for hydrazoic acid in many reactions. A notable example is the cycloaddition of hydrazoic acid to acetylenes which is a general route to substituted triazoles.4 The reaction of trimethylsilyl azide with acetylenes is also a general reaction from which the 2-trimethyIsilyI-1,2,3-triazoles may be obtained in good yield.5 On hydrolysis these adducts are converted under mild conditions to the parent alkyl 1,2,3-triazoles.5... 

Selective phosphonate ester dealkylation. Alkyl phosphonate esters are selectively and nearly quantitatively cleaved by bromotrimethylsilane in the presence of alkyl carboxylate esters, carbamates, acetylenes, ketones, and halides. Alkyl iodides do not exchange under the reaction conditions. The resulting bis(trimethylsilyl) phosphonates are hydrolyzed in acetone by a small excess of water. 

Since the report by Carboni and Lindsey in 1959 on the cycloaddition reaction of tetrazines to multiple bonded molecules as a route to pyridazines, such reactions have been extensively studied. In addition to acetylenes and ethylenes, enol ethers, ketene acetals, enol esters and enamines, and even aldehydes and ketones have been used as starting materials for pyridazines. A detailed investigation of various 1,2,4, 5-tetrazines in these syntheses revealed the following facts. In [4 + 2] cycloaddition reactions of 3,6-bis(methylthio)-l,2,4,5-tetrazine with dienophiles, which lead to pyridazines, the following order of reactivity was observed (in parenthesis the reaction temperature is given) ynamines (25°C) > enamines (25-60°C) > ketene acetals (45-100°C) > enamides (80-100°C) > trimethylsilyl or alkyl enol ethers (100-140°C) > enol... 

The preferred catalysts for the one-step co-cyclization of acetylene and acetonitrile (or alkyl cyanides in general) to give a-picoline (or 2-alkylpyridines) are i/ -Cp-cobalt cod or / -trimethylsilyl-Cp-cobalt cod (eq. (2)). The a-picoline synthesis is best performed in pure nitrile without any additional solvent [5 d]. 

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